Bandwidth Calculator: Download Time, Hosting Needs & Data Caps
Estimate download times, plan website hosting bandwidth, and convert monthly data caps to Mbps. Bits vs bytes, Binary vs Decimal. Free bandwidth and download time calculator.
What This Tool Does
Three modules in one: Download/Upload Timeโplug in file size and connection speed; get theoretical and real-world times with adjustable overhead. Website Hosting Plannerโpage views, average page size, and redundancy factor yield required monthly bandwidth and minimum line speed. Hosting Bandwidth Converterโturn a cap like โ2 TB/monthโ into the equivalent sustained Mbps, or the other way around.
Bits vs Bytes: The 8x Rule
Speed is quoted in bits per second: Mbps, Kbps, Gbps. File size is in bytes: MB, GB, TB. One byte = 8 bits, so . A 100 Mbps link can move 12.5 MB per second in theory. Confusing bits and bytesโe.g. treating 100 Mbps as 100 MB/sโthrows results off by a factor of 8. Lowercase b = bits; uppercase B = bytes.
Binary (1024) vs Decimal (1000)
Operating systems and RAM traditionally use Base-2: 1 KB = 1024 bytes, 1 MB = 1024ยฒ, and so on. Storage and network vendors often use Base-10: 1 KB = 1000 bytes. A drive sold as โ1 TBโ (10ยนยฒ bytes) shows about 931 GB in Windows because 1024โด โ 1000โด. When estimating downloads or comparing caps, pick the base that matches your source.
Why Advertised Speed โ Real Throughput
TCP and IP headers, retransmissions, and link-layer framing consume bandwidth that never shows up as โfile data.โ Plan for roughly 85% of the advertised lineโso 100 Mbps behaves more like 10โ11 MB/s sustained. The 10โ20% overhead slider lets you model this; 15% is a solid default for most home connections.
Converting Monthly Caps to Sustained Speed
A 2 TB/month cap over 30 days (2,592,000 seconds) equals running flat. Hosting and mobile plans quote caps; this formula answers โwhat constant speed would use that cap?โ The converter handles both directions: cap โ speed and speed โ cap.
Bandwidth Calculator FAQ
? Why does my 100 Mbps plan only download at about 12 MB/s?
ISPs advertise in megabits per second; your OS shows megabytes. Since 1 byte = 8 bits, 100 Mbps converts to in a vacuum. In practice, TCP/IP headers, retransmissions, and WiโFi interference chew up 10โ20% of that. Expect ~10โ11 MB/s on a solid connection. The overhead slider models this gap.
? Should I use Binary (1024) or Decimal (1000) for file sizes?
Depends whoโs measuring. Windows and most OSes use Binary: 1 KB = 1024 bytes, so a โ1 TBโ drive shows ~931 GB. ISPs and hosting providers use Decimal: 1 KB = 1000 bytes. A 2 TB data cap is 2 trillion bytes. Toggle the base so your results align with the source youโre comparing against.
? How do I figure out what speed a 2 TB/month cap equals?
That cap is equivalent to a constant over 30 days. The math: Mbps (2.59M seconds in 30 days). Hosting and mobile plans quote caps; this shows the โalways onโ speed that would use that cap if it ran flat.
? What redundancy factor do I need for a small blog?
A 1.2ร factor adds ~20% headroom for normal daily spikes. For a blog or portfolio, thatโs usually enough. Bump to 1.5ร or 2ร if you run promos, launches, or anything that could double traffic in an hour. Under-provisioning leads to throttling and timeouts when everyone hits the site at once.
? Why is there a "Real-World" estimate separate from theoretical time?
Theoretical assumes every bit is file data. Real-world accounts for protocol overheadโTCP and IP headers, retransmits, and congestion windows. A 70 GB game โshouldโ take ~1h33m at 100 Mbps; with 15% overhead itโs closer to 1h48m. The slider lets you tune that overhead to match what you see on your network.