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Tech & wiring

IP Subnet Calculator: CIDR, Mask & Host Range

This calculator derives IPv4 network, broadcast, and usable host range from an IP address and CIDR prefix using bitwise AND/OR on the 32-bit mask, and shows IPv6 network bounds and address counts for prefixes up to /128. A binary visualizer and /8–/32 cheat sheet map prefix length to dotted masks. It does not scan your LAN or validate BGP routing—only the math for the address you enter.

By Jeff Beem

Updated

IP version
🌐

Subnet Calculator

Network class

Filters subnet mask options (classful reference). “Any” lists /1–/32.

IP address (binary)
11000000·10101000·00000001·00000000
Subnet mask (binary)

1s = network bits (slate), 0s = host bits (green). A /24 uses exactly 3 octets.

11111111·11111111·11111111·00000000

/24 subnets in the same parent span as 192.168.*.*256 total

NetworkUsable host rangeBroadcast
192.168.0.0192.168.0.1 - 192.168.0.254192.168.0.255
192.168.1.0192.168.1.1 - 192.168.1.254192.168.1.255
192.168.2.0192.168.2.1 - 192.168.2.254192.168.2.255
192.168.3.0192.168.3.1 - 192.168.3.254192.168.3.255
192.168.4.0192.168.4.1 - 192.168.4.254192.168.4.255
192.168.5.0192.168.5.1 - 192.168.5.254192.168.5.255
192.168.6.0192.168.6.1 - 192.168.6.254192.168.6.255
192.168.7.0192.168.7.1 - 192.168.7.254192.168.7.255
192.168.8.0192.168.8.1 - 192.168.8.254192.168.8.255
192.168.9.0192.168.9.1 - 192.168.9.254192.168.9.255
192.168.10.0192.168.10.1 - 192.168.10.254192.168.10.255
192.168.11.0192.168.11.1 - 192.168.11.254192.168.11.255
192.168.12.0192.168.12.1 - 192.168.12.254192.168.12.255
192.168.13.0192.168.13.1 - 192.168.13.254192.168.13.255
192.168.14.0192.168.14.1 - 192.168.14.254192.168.14.255
192.168.15.0192.168.15.1 - 192.168.15.254192.168.15.255
192.168.16.0192.168.16.1 - 192.168.16.254192.168.16.255
192.168.17.0192.168.17.1 - 192.168.17.254192.168.17.255
192.168.18.0192.168.18.1 - 192.168.18.254192.168.18.255
192.168.19.0192.168.19.1 - 192.168.19.254192.168.19.255
192.168.20.0192.168.20.1 - 192.168.20.254192.168.20.255
192.168.21.0192.168.21.1 - 192.168.21.254192.168.21.255
192.168.22.0192.168.22.1 - 192.168.22.254192.168.22.255
192.168.23.0192.168.23.1 - 192.168.23.254192.168.23.255
192.168.24.0192.168.24.1 - 192.168.24.254192.168.24.255
192.168.25.0192.168.25.1 - 192.168.25.254192.168.25.255
192.168.26.0192.168.26.1 - 192.168.26.254192.168.26.255
192.168.27.0192.168.27.1 - 192.168.27.254192.168.27.255
192.168.28.0192.168.28.1 - 192.168.28.254192.168.28.255
192.168.29.0192.168.29.1 - 192.168.29.254192.168.29.255
192.168.30.0192.168.30.1 - 192.168.30.254192.168.30.255
192.168.31.0192.168.31.1 - 192.168.31.254192.168.31.255
192.168.32.0192.168.32.1 - 192.168.32.254192.168.32.255
192.168.33.0192.168.33.1 - 192.168.33.254192.168.33.255
192.168.34.0192.168.34.1 - 192.168.34.254192.168.34.255
192.168.35.0192.168.35.1 - 192.168.35.254192.168.35.255
192.168.36.0192.168.36.1 - 192.168.36.254192.168.36.255
192.168.37.0192.168.37.1 - 192.168.37.254192.168.37.255
192.168.38.0192.168.38.1 - 192.168.38.254192.168.38.255
192.168.39.0192.168.39.1 - 192.168.39.254192.168.39.255
192.168.40.0192.168.40.1 - 192.168.40.254192.168.40.255
192.168.41.0192.168.41.1 - 192.168.41.254192.168.41.255
192.168.42.0192.168.42.1 - 192.168.42.254192.168.42.255
192.168.43.0192.168.43.1 - 192.168.43.254192.168.43.255
192.168.44.0192.168.44.1 - 192.168.44.254192.168.44.255
192.168.45.0192.168.45.1 - 192.168.45.254192.168.45.255
192.168.46.0192.168.46.1 - 192.168.46.254192.168.46.255
192.168.47.0192.168.47.1 - 192.168.47.254192.168.47.255
192.168.48.0192.168.48.1 - 192.168.48.254192.168.48.255
192.168.49.0192.168.49.1 - 192.168.49.254192.168.49.255
192.168.50.0192.168.50.1 - 192.168.50.254192.168.50.255
192.168.51.0192.168.51.1 - 192.168.51.254192.168.51.255
192.168.52.0192.168.52.1 - 192.168.52.254192.168.52.255
192.168.53.0192.168.53.1 - 192.168.53.254192.168.53.255
192.168.54.0192.168.54.1 - 192.168.54.254192.168.54.255
192.168.55.0192.168.55.1 - 192.168.55.254192.168.55.255
192.168.56.0192.168.56.1 - 192.168.56.254192.168.56.255
192.168.57.0192.168.57.1 - 192.168.57.254192.168.57.255
192.168.58.0192.168.58.1 - 192.168.58.254192.168.58.255
192.168.59.0192.168.59.1 - 192.168.59.254192.168.59.255
192.168.60.0192.168.60.1 - 192.168.60.254192.168.60.255
192.168.61.0192.168.61.1 - 192.168.61.254192.168.61.255
192.168.62.0192.168.62.1 - 192.168.62.254192.168.62.255
192.168.63.0192.168.63.1 - 192.168.63.254192.168.63.255
192.168.64.0192.168.64.1 - 192.168.64.254192.168.64.255
192.168.65.0192.168.65.1 - 192.168.65.254192.168.65.255
192.168.66.0192.168.66.1 - 192.168.66.254192.168.66.255
192.168.67.0192.168.67.1 - 192.168.67.254192.168.67.255
192.168.68.0192.168.68.1 - 192.168.68.254192.168.68.255
192.168.69.0192.168.69.1 - 192.168.69.254192.168.69.255
192.168.70.0192.168.70.1 - 192.168.70.254192.168.70.255
192.168.71.0192.168.71.1 - 192.168.71.254192.168.71.255
192.168.72.0192.168.72.1 - 192.168.72.254192.168.72.255
192.168.73.0192.168.73.1 - 192.168.73.254192.168.73.255
192.168.74.0192.168.74.1 - 192.168.74.254192.168.74.255
192.168.75.0192.168.75.1 - 192.168.75.254192.168.75.255
192.168.76.0192.168.76.1 - 192.168.76.254192.168.76.255
192.168.77.0192.168.77.1 - 192.168.77.254192.168.77.255
192.168.78.0192.168.78.1 - 192.168.78.254192.168.78.255
192.168.79.0192.168.79.1 - 192.168.79.254192.168.79.255
192.168.80.0192.168.80.1 - 192.168.80.254192.168.80.255
192.168.81.0192.168.81.1 - 192.168.81.254192.168.81.255
192.168.82.0192.168.82.1 - 192.168.82.254192.168.82.255
192.168.83.0192.168.83.1 - 192.168.83.254192.168.83.255
192.168.84.0192.168.84.1 - 192.168.84.254192.168.84.255
192.168.85.0192.168.85.1 - 192.168.85.254192.168.85.255
192.168.86.0192.168.86.1 - 192.168.86.254192.168.86.255
192.168.87.0192.168.87.1 - 192.168.87.254192.168.87.255
192.168.88.0192.168.88.1 - 192.168.88.254192.168.88.255
192.168.89.0192.168.89.1 - 192.168.89.254192.168.89.255
192.168.90.0192.168.90.1 - 192.168.90.254192.168.90.255
192.168.91.0192.168.91.1 - 192.168.91.254192.168.91.255
192.168.92.0192.168.92.1 - 192.168.92.254192.168.92.255
192.168.93.0192.168.93.1 - 192.168.93.254192.168.93.255
192.168.94.0192.168.94.1 - 192.168.94.254192.168.94.255
192.168.95.0192.168.95.1 - 192.168.95.254192.168.95.255
192.168.96.0192.168.96.1 - 192.168.96.254192.168.96.255
192.168.97.0192.168.97.1 - 192.168.97.254192.168.97.255
192.168.98.0192.168.98.1 - 192.168.98.254192.168.98.255
192.168.99.0192.168.99.1 - 192.168.99.254192.168.99.255
192.168.100.0192.168.100.1 - 192.168.100.254192.168.100.255
192.168.101.0192.168.101.1 - 192.168.101.254192.168.101.255
192.168.102.0192.168.102.1 - 192.168.102.254192.168.102.255
192.168.103.0192.168.103.1 - 192.168.103.254192.168.103.255
192.168.104.0192.168.104.1 - 192.168.104.254192.168.104.255
192.168.105.0192.168.105.1 - 192.168.105.254192.168.105.255
192.168.106.0192.168.106.1 - 192.168.106.254192.168.106.255
192.168.107.0192.168.107.1 - 192.168.107.254192.168.107.255
192.168.108.0192.168.108.1 - 192.168.108.254192.168.108.255
192.168.109.0192.168.109.1 - 192.168.109.254192.168.109.255
192.168.110.0192.168.110.1 - 192.168.110.254192.168.110.255
192.168.111.0192.168.111.1 - 192.168.111.254192.168.111.255
192.168.112.0192.168.112.1 - 192.168.112.254192.168.112.255
192.168.113.0192.168.113.1 - 192.168.113.254192.168.113.255
192.168.114.0192.168.114.1 - 192.168.114.254192.168.114.255
192.168.115.0192.168.115.1 - 192.168.115.254192.168.115.255
192.168.116.0192.168.116.1 - 192.168.116.254192.168.116.255
192.168.117.0192.168.117.1 - 192.168.117.254192.168.117.255
192.168.118.0192.168.118.1 - 192.168.118.254192.168.118.255
192.168.119.0192.168.119.1 - 192.168.119.254192.168.119.255
192.168.120.0192.168.120.1 - 192.168.120.254192.168.120.255
192.168.121.0192.168.121.1 - 192.168.121.254192.168.121.255
192.168.122.0192.168.122.1 - 192.168.122.254192.168.122.255
192.168.123.0192.168.123.1 - 192.168.123.254192.168.123.255
192.168.124.0192.168.124.1 - 192.168.124.254192.168.124.255
192.168.125.0192.168.125.1 - 192.168.125.254192.168.125.255
192.168.126.0192.168.126.1 - 192.168.126.254192.168.126.255
192.168.127.0192.168.127.1 - 192.168.127.254192.168.127.255
192.168.128.0192.168.128.1 - 192.168.128.254192.168.128.255
192.168.129.0192.168.129.1 - 192.168.129.254192.168.129.255
192.168.130.0192.168.130.1 - 192.168.130.254192.168.130.255
192.168.131.0192.168.131.1 - 192.168.131.254192.168.131.255
192.168.132.0192.168.132.1 - 192.168.132.254192.168.132.255
192.168.133.0192.168.133.1 - 192.168.133.254192.168.133.255
192.168.134.0192.168.134.1 - 192.168.134.254192.168.134.255
192.168.135.0192.168.135.1 - 192.168.135.254192.168.135.255
192.168.136.0192.168.136.1 - 192.168.136.254192.168.136.255
192.168.137.0192.168.137.1 - 192.168.137.254192.168.137.255
192.168.138.0192.168.138.1 - 192.168.138.254192.168.138.255
192.168.139.0192.168.139.1 - 192.168.139.254192.168.139.255
192.168.140.0192.168.140.1 - 192.168.140.254192.168.140.255
192.168.141.0192.168.141.1 - 192.168.141.254192.168.141.255
192.168.142.0192.168.142.1 - 192.168.142.254192.168.142.255
192.168.143.0192.168.143.1 - 192.168.143.254192.168.143.255
192.168.144.0192.168.144.1 - 192.168.144.254192.168.144.255
192.168.145.0192.168.145.1 - 192.168.145.254192.168.145.255
192.168.146.0192.168.146.1 - 192.168.146.254192.168.146.255
192.168.147.0192.168.147.1 - 192.168.147.254192.168.147.255
192.168.148.0192.168.148.1 - 192.168.148.254192.168.148.255
192.168.149.0192.168.149.1 - 192.168.149.254192.168.149.255
192.168.150.0192.168.150.1 - 192.168.150.254192.168.150.255
192.168.151.0192.168.151.1 - 192.168.151.254192.168.151.255
192.168.152.0192.168.152.1 - 192.168.152.254192.168.152.255
192.168.153.0192.168.153.1 - 192.168.153.254192.168.153.255
192.168.154.0192.168.154.1 - 192.168.154.254192.168.154.255
192.168.155.0192.168.155.1 - 192.168.155.254192.168.155.255
192.168.156.0192.168.156.1 - 192.168.156.254192.168.156.255
192.168.157.0192.168.157.1 - 192.168.157.254192.168.157.255
192.168.158.0192.168.158.1 - 192.168.158.254192.168.158.255
192.168.159.0192.168.159.1 - 192.168.159.254192.168.159.255
192.168.160.0192.168.160.1 - 192.168.160.254192.168.160.255
192.168.161.0192.168.161.1 - 192.168.161.254192.168.161.255
192.168.162.0192.168.162.1 - 192.168.162.254192.168.162.255
192.168.163.0192.168.163.1 - 192.168.163.254192.168.163.255
192.168.164.0192.168.164.1 - 192.168.164.254192.168.164.255
192.168.165.0192.168.165.1 - 192.168.165.254192.168.165.255
192.168.166.0192.168.166.1 - 192.168.166.254192.168.166.255
192.168.167.0192.168.167.1 - 192.168.167.254192.168.167.255
192.168.168.0192.168.168.1 - 192.168.168.254192.168.168.255
192.168.169.0192.168.169.1 - 192.168.169.254192.168.169.255
192.168.170.0192.168.170.1 - 192.168.170.254192.168.170.255
192.168.171.0192.168.171.1 - 192.168.171.254192.168.171.255
192.168.172.0192.168.172.1 - 192.168.172.254192.168.172.255
192.168.173.0192.168.173.1 - 192.168.173.254192.168.173.255
192.168.174.0192.168.174.1 - 192.168.174.254192.168.174.255
192.168.175.0192.168.175.1 - 192.168.175.254192.168.175.255
192.168.176.0192.168.176.1 - 192.168.176.254192.168.176.255
192.168.177.0192.168.177.1 - 192.168.177.254192.168.177.255
192.168.178.0192.168.178.1 - 192.168.178.254192.168.178.255
192.168.179.0192.168.179.1 - 192.168.179.254192.168.179.255
192.168.180.0192.168.180.1 - 192.168.180.254192.168.180.255
192.168.181.0192.168.181.1 - 192.168.181.254192.168.181.255
192.168.182.0192.168.182.1 - 192.168.182.254192.168.182.255
192.168.183.0192.168.183.1 - 192.168.183.254192.168.183.255
192.168.184.0192.168.184.1 - 192.168.184.254192.168.184.255
192.168.185.0192.168.185.1 - 192.168.185.254192.168.185.255
192.168.186.0192.168.186.1 - 192.168.186.254192.168.186.255
192.168.187.0192.168.187.1 - 192.168.187.254192.168.187.255
192.168.188.0192.168.188.1 - 192.168.188.254192.168.188.255
192.168.189.0192.168.189.1 - 192.168.189.254192.168.189.255
192.168.190.0192.168.190.1 - 192.168.190.254192.168.190.255
192.168.191.0192.168.191.1 - 192.168.191.254192.168.191.255
192.168.192.0192.168.192.1 - 192.168.192.254192.168.192.255
192.168.193.0192.168.193.1 - 192.168.193.254192.168.193.255
192.168.194.0192.168.194.1 - 192.168.194.254192.168.194.255
192.168.195.0192.168.195.1 - 192.168.195.254192.168.195.255
192.168.196.0192.168.196.1 - 192.168.196.254192.168.196.255
192.168.197.0192.168.197.1 - 192.168.197.254192.168.197.255
192.168.198.0192.168.198.1 - 192.168.198.254192.168.198.255
192.168.199.0192.168.199.1 - 192.168.199.254192.168.199.255
192.168.200.0192.168.200.1 - 192.168.200.254192.168.200.255
192.168.201.0192.168.201.1 - 192.168.201.254192.168.201.255
192.168.202.0192.168.202.1 - 192.168.202.254192.168.202.255
192.168.203.0192.168.203.1 - 192.168.203.254192.168.203.255
192.168.204.0192.168.204.1 - 192.168.204.254192.168.204.255
192.168.205.0192.168.205.1 - 192.168.205.254192.168.205.255
192.168.206.0192.168.206.1 - 192.168.206.254192.168.206.255
192.168.207.0192.168.207.1 - 192.168.207.254192.168.207.255
192.168.208.0192.168.208.1 - 192.168.208.254192.168.208.255
192.168.209.0192.168.209.1 - 192.168.209.254192.168.209.255
192.168.210.0192.168.210.1 - 192.168.210.254192.168.210.255
192.168.211.0192.168.211.1 - 192.168.211.254192.168.211.255
192.168.212.0192.168.212.1 - 192.168.212.254192.168.212.255
192.168.213.0192.168.213.1 - 192.168.213.254192.168.213.255
192.168.214.0192.168.214.1 - 192.168.214.254192.168.214.255
192.168.215.0192.168.215.1 - 192.168.215.254192.168.215.255
192.168.216.0192.168.216.1 - 192.168.216.254192.168.216.255
192.168.217.0192.168.217.1 - 192.168.217.254192.168.217.255
192.168.218.0192.168.218.1 - 192.168.218.254192.168.218.255
192.168.219.0192.168.219.1 - 192.168.219.254192.168.219.255
192.168.220.0192.168.220.1 - 192.168.220.254192.168.220.255
192.168.221.0192.168.221.1 - 192.168.221.254192.168.221.255
192.168.222.0192.168.222.1 - 192.168.222.254192.168.222.255
192.168.223.0192.168.223.1 - 192.168.223.254192.168.223.255
192.168.224.0192.168.224.1 - 192.168.224.254192.168.224.255
192.168.225.0192.168.225.1 - 192.168.225.254192.168.225.255
192.168.226.0192.168.226.1 - 192.168.226.254192.168.226.255
192.168.227.0192.168.227.1 - 192.168.227.254192.168.227.255
192.168.228.0192.168.228.1 - 192.168.228.254192.168.228.255
192.168.229.0192.168.229.1 - 192.168.229.254192.168.229.255
192.168.230.0192.168.230.1 - 192.168.230.254192.168.230.255
192.168.231.0192.168.231.1 - 192.168.231.254192.168.231.255
192.168.232.0192.168.232.1 - 192.168.232.254192.168.232.255
192.168.233.0192.168.233.1 - 192.168.233.254192.168.233.255
192.168.234.0192.168.234.1 - 192.168.234.254192.168.234.255
192.168.235.0192.168.235.1 - 192.168.235.254192.168.235.255
192.168.236.0192.168.236.1 - 192.168.236.254192.168.236.255
192.168.237.0192.168.237.1 - 192.168.237.254192.168.237.255
192.168.238.0192.168.238.1 - 192.168.238.254192.168.238.255
192.168.239.0192.168.239.1 - 192.168.239.254192.168.239.255
192.168.240.0192.168.240.1 - 192.168.240.254192.168.240.255
192.168.241.0192.168.241.1 - 192.168.241.254192.168.241.255
192.168.242.0192.168.242.1 - 192.168.242.254192.168.242.255
192.168.243.0192.168.243.1 - 192.168.243.254192.168.243.255
192.168.244.0192.168.244.1 - 192.168.244.254192.168.244.255
192.168.245.0192.168.245.1 - 192.168.245.254192.168.245.255
192.168.246.0192.168.246.1 - 192.168.246.254192.168.246.255
192.168.247.0192.168.247.1 - 192.168.247.254192.168.247.255
192.168.248.0192.168.248.1 - 192.168.248.254192.168.248.255
192.168.249.0192.168.249.1 - 192.168.249.254192.168.249.255
192.168.250.0192.168.250.1 - 192.168.250.254192.168.250.255
192.168.251.0192.168.251.1 - 192.168.251.254192.168.251.255
192.168.252.0192.168.252.1 - 192.168.252.254192.168.252.255
192.168.253.0192.168.253.1 - 192.168.253.254192.168.253.255
192.168.254.0192.168.254.1 - 192.168.254.254192.168.254.255
192.168.255.0192.168.255.1 - 192.168.255.254192.168.255.255

How to use this calculator

Enter an IPv4 address and pick a CIDR prefix with the dropdown or slider. The results card shows network, broadcast, usable range, mask, and host counts; binary rows under the inputs mark network bits blue and host bits green. Detect My IP fills your public address on load; Clear resets to 192.168.1.0/24. Click a row in the Typical subnets table to apply /8–/32 prefixes or filter by host count. IPv4 math is bitwise AND/OR on a 32-bit mask; /31 and /32 are special cases with one or zero usable hosts. This tool does not ping your LAN or validate routing tables.

Typical subnets

Click a row to apply that prefix to the calculator. Search by prefix (/24), mask, or hosts (e.g. 500).

PrefixSubnet maskUsable hosts
/8255.0.0.016,777,214
/9255.128.0.08,388,606
/10255.192.0.04,194,302
/11255.224.0.02,097,150
/12255.240.0.01,048,574
/13255.248.0.0524,286
/14255.252.0.0262,142
/15255.254.0.0131,070
/16255.255.0.065,534
/17255.255.128.032,766
/18255.255.192.016,382
/19255.255.224.08,190
/20255.255.240.04,094
/21255.255.248.02,046
/22255.255.252.01,022
/23255.255.254.0510
/24255.255.255.0254
/25255.255.255.128126
/26255.255.255.19262
/27255.255.255.22430
/28255.255.255.24014
/29255.255.255.2486
/30255.255.255.2522
/31255.255.255.2542
/32255.255.255.2550

Reading the subnet results panel

Match the dark results card to your inputs: network, broadcast, and usable range on IPv4; network and range end on IPv6. Binary rows under the form show where the prefix splits network from host bits.

Example: 192.168.1.0/24 (private LAN)

After Clear: IP 192.168.1.0, prefix /24, mask 255.255.255.0, wildcard 0.0.0.255. Network 192.168.1.0, broadcast 192.168.1.255, usable 192.168.1.1 – 192.168.1.254 (254 of 256 addresses). Type badge Private, class C. Technical block adds integer 3232235776, hex 0xc0a80100, and 6to4 2002:c0a8:100::/48.

Same subnet, different host IP

Type 192.168.1.50 on the same /24: network and broadcast stay fixed; only the host bits in the IP binary row change. Assignable addresses remain .1 through .254—the usable range line in the panel.

Prefix cheat sheet, slider, and class filter

Click any /8–/32 row in the Typical subnets table in the calculator shell to set CIDR. Filter by prefix or host count. The range slider under the Subnet dropdown tracks the same value. Class A/B/C only narrows dropdown bounds—it does not change live routing.

IPv6 tab: 2001:db8::1/64

Network 2001:db8::; range ends 2001:db8::ffff:ffff:ffff:ffff; 18,446,744,073,709,551,616 addresses in the prefix. Hextet cards color routing prefix versus interface ID; no broadcast line.

Sibling subnet table (IPv4)

Below the main results, the table lists equal-sized /n subnets that share the same parent /8, /16, or /24 span as your input. Each row shows network, usable range, and broadcast for that slice. Large parent blocks truncate at 512 rows—the header still reports the full count.

IP subnet calculator: CIDR, mask, and host range

Bitwise IPv4 and IPv6 subnet math in the browser. Does not ping networks, scan LANs, or validate BGP routing.

What this calculator does

Given an IPv4 address and CIDR prefix, it returns network and broadcast addresses, first and last usable hosts, subnet and wildcard masks, host counts, and class/type labels, plus optional public-IP detection on load. IPv6 mode adds expanded and compressed notation, prefix bounds, and hextet coloring. A binary visualizer and clickable prefix table are built into the form—not separate theory blocks.

How the math works

IPv4 treats the address as a 32-bit integer. Prefix length n fixes the top n bits as network. For most subnets, usable hosts =
Usable hosts=2(32−n)−2\text{Usable hosts} = 2^{(32 - n)} - 2
because the all-zeroes and all-ones host values are reserved (network ID and broadcast). Network = IP AND mask; broadcast = IP OR (NOT mask). IPv6 uses 128 bits; addresses in a prefix = 2(128−n)2^{(128-n)} with no broadcast subtraction. Compression follows RFC 5952 (longest run of zero hextets replaced once by ::). /31 shows two usable hosts in this tool; /32 is one host.
  • IPv6 link size:
    /64 is the usual LAN prefix (SLAAC expects it on most interfaces). /48 and /56 are common allocation sizes from ISPs—the quick buttons in the IPv6 sidebar apply those prefixes.
  • Hex and hextets:
    Each hextet is 16 bits (four hex digits). Reading expanded form makes prefix boundaries visible when compressed :: notation hides zero runs.

Edge cases and enumeration limits

Several behaviors are easy to miss because they only show up at extreme prefix lengths or large parent blocks.
  • /31 and /32:
    /32 returns a single host—network and broadcast collapse to the same address. /31 shows two usable hosts in this tool (RFC 3021 point-to-point links). There is no /0 in the dropdown.
  • Sibling subnet table:
    Lists equal-sized /n subnets sharing the same enclosing /8, /16, or /24 parent as your input. A /26 inside 192.168.1.0/24 yields four rows (.0, .64, .128, .192). Output stops at 512 rows when the math would produce more; the header still shows the full count.
  • Class filter vs CIDR:
    Class A/B/C only changes dropdown bounds (/8–/30, /16–/30, /24–/30). It does not validate whether your address is “really” classful—modern routing ignores that label.
  • Invalid or detected IPs:
    Malformed IPv4 shows a prompt instead of results. Public-IP detection on load uses an external API; failure falls back to 192.168.1.1 with an error note—Clear restores the private example.

IP Subnet Calculator FAQ

How does this page compute the network and broadcast addresses?

IPv4: bitwise AND with the CIDR mask yields the network address; OR with the inverted mask yields broadcast. IPv6: host bits beyond your prefix are cleared—there is no broadcast row. See the Example: 192.168.1.0/24 card for a full IPv4 walk-through; the IPv6 tab opens at 2001:db8::1/64.

Why does a /24 show 254 usable hosts instead of 256?

Two IPv4 addresses are reserved per subnet: all host bits 0 (network ID) and all host bits 1 (broadcast). For /1–/30 the panel uses 2(32−n)−22^{(32-n)} - 2. /31 lists 2 usable hosts here (RFC 3021 point-to-point); /32 is one host.

What do the blue and green bits in the binary visualizer mean?

Blue = network portion from your CIDR prefix; green = host bits. The mask row uses the same colors (ones = network). Move the prefix slider or pick a cheat-sheet row to watch the split shift—/24 aligns on an octet boundary; /25 does not.

What changes when I switch to the IPv6 tab?

No broadcast or −2 host math. You get expanded and compressed forms, network and range-end addresses, total address count, and hextet cards (routing prefix vs interface ID). Sidebar buttons jump to /48, /56, or /64.

What does the network class filter do?

It only limits the CIDR dropdown (Class A from /8, B from /16, C from /24). CIDR is classless; the filter is a study aid, not routing policy. Use Any for the full /1–/32 list.

Why did my IP address change when the page loaded?

The widget fetches your public IPv4 on load and drops it into the field (prefix stays /24 until you change it). That is a convenience, not an assignment. Clear resets to 192.168.1.0/24.

What are the integer, hex, and reverse-DNS fields for?

They are alternate views of the same 32-bit IPv4 value: decimal ID, hex ID, in-addr.arpa reverse zone, IPv4-mapped IPv6 (::ffff:…), and a 2002:…::/48 6to4 prefix derived from the address. The page does not publish DNS records or verify they exist on the internet.

What is the wildcard mask on the results card?

The inverse of the subnet mask: ones mark host bits, zeros mark network bits. Cisco-style ACLs and some routing configs use wildcard notation instead of dotted masks. At /24 the wildcard reads 0.0.0.255; it changes only when you change the prefix, not when you type a different host IP in the same subnet.

When should I trust the /31 host count?

RFC 3021 allows two addresses on a /31 point-to-point link (no traditional broadcast). This tool lists 2 usable hosts at /31 to match that convention. If your platform still treats both addresses as reserved, treat the row as documentation-only and follow your vendor’s guide.

How is this different from the Binary Calculator?

This page is subnetting end-to-end: CIDR, mask, ranges, and IPv6 prefix layout. The Binary Calculator handles bitwise ops and base conversion on bit patterns you already have.

Mathematical Reference Note

Calculation Logic: This tool uses standard mathematical algorithms. While we strive for accuracy, errors in logic or user input can result in incorrect data.

Verification: Results should be cross-checked if used for important academic, professional, or personal calculations.

Standard Terms: This tool is provided free of charge and as-is. CalcRegistry provides no warranty regarding the accuracy or fitness of these results for your specific needs.

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