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Concrete & cubic yards

Concrete Calculator

Calculate how many cubic yards or bags of concrete you need for slabs, footings, columns, and stairs. Enter your dimensions, choose a shape, and get the volume with an adjustable waste factor to account for spillage and overage.

By Jeff Beem

Updated

Project dimensions

Slab dimensions: length, width, thickness
10%

Add 5–10% for spillage and uneven subgrade

Results
0.90

Cubic yards

Cubic feet24.28
Cubic meters0.69

Bagged concrete

40 lb bags82
60 lb bags53
80 lb bags41
Estimated weight1.80 tons (3,597 lbs)

Based on 4,000 lbs per cubic yard

Concrete Calculator: Bags, Yards, and Why the Math Isn't Enough

Get volumes for slabs, footings, columns, stairs, and curbs. We add a waste factor so you don't run short, and show both bag counts and cubic yards so you can compare bagged vs. ready-mix.

What Actually Eats Your Concrete

Why Pros Add Waste

Uneven subgrade, spillage, and over-excavation eat into every pour. If you order exactly what the formula says, you'll run short. A 5–10% buffer covers it; go to 15–20% for stairs, columns, or tight spots. Running out mid-pour means cold joints and rework.

Bags vs. Truck

Bags make sense under a yard, no minimum, you mix as you go. Once you're past a yard, ready-mix usually wins on price and speed. Most suppliers have a 1-yard minimum, so small jobs stay in bags.

Weight Matters

Concrete runs about 4,000 lbs per cubic yard. That affects which truck can reach your site and whether your base can take the load. Worth checking before you schedule the pour.

Slabs + Columns + Stairs

Do each shape separately, add the volumes, then apply one waste factor to the total. No need to guess per shape, one buffer for the whole job.

Concrete Calculator: Estimate Bags & Cubic Yards for Your Project

Free concrete calculator for slabs, footings, columns, stairs, and curbs. Get bag counts and cubic yards with a waste factor built in. Imperial and metric.

What This Calculator Does

This concrete calculator estimates the volume of concrete needed for slabs, footings, round columns, stairs, and curbs, then converts that volume into bag counts and cubic yards (or cubic meters). It is designed for homeowners planning a DIY pour, contractors preparing material orders, and anyone who needs to decide between buying bags and calling for a ready-mix truck. The tool outputs total volume with a configurable waste factor (5–20%), bag counts for 40 lb, 60 lb, and 80 lb mixes, estimated weight of the pour, and a comparison of bagged versus ready-mix options. It does not specify concrete mix design, rebar spacing, or curing schedules. Enter dimensions in imperial or metric units and the calculator handles all conversions.

How to Use This Calculator

Choose the project shape from the selector: slab or footing, round column, stairs, or curb and gutter. Enter the dimensions in your preferred unitsβ€”length, width, and thickness for slabs; diameter and height for columns; run, rise, width, and step count for stairs. Set the waste factor: 5% for simple slabs on level ground, 10% for most residential work (the default), or 15–20% for stairs, columns, and tight spots. The results panel shows total volume in cubic yards (or cubic meters), bag counts for three bag sizes, and the estimated weight of the pour. Compare the bag count against the one-cubic-yard minimum for ready-mix delivery to decide the most cost-effective ordering method for your job.

How Much Concrete Do I Really Need?

Why the Math Isn't Enough

Ordering exactly what the formula gives you often leads to running short. Subgrade isn't perfectly level, concrete spills, and forms get overfilled. Contractors add a waste factor to cover it.
  • Uneven ground:
    Low spots and rough subgrade eat extra concrete to keep thickness consistent.
  • Spillage and over-excavation:
    You lose some in the chute and sometimes overfill forms to get full coverage.
  • What to do:
    Add a buffer, we let you set 0–20%, default 10%, so you order enough without guessing.

How Much Waste to Add

It depends on the job.
  • Simple slabs (5%):
    Level site, straightforward forms. Patios, small driveways.
  • Most residential (10%):
    Our default. Covers typical subgrade and spillage.
  • Stairs, columns, tight spots (15–20%):
    More formwork, more waste. Bump it up so you don't run out.

Concrete Volume by Project Type

Slabs and Footings

Length Γ— width Γ— thickness. Same units for all three.
  • Formula:
    V = L Γ— W Γ— T

    where V is volume, L is length, W is width, and T is thickness (all in same units).

  • Example:
    10 ft Γ— 10 ft at 4 in thick: 10 Γ— 10 Γ— (4/12) = 33.33 cubic feet β‰ˆ 1.23 cubic yards.
  • Rough thickness:
    Driveways 4–6 in. Patios and sidewalks 4 in. Foundations 6–8 in.

Round Columns

Cylinder volume: Ο€ Γ— radiusΒ² Γ— height. Radius = diameter Γ· 2.
  • Formula:
    V = Ο€ Γ— r2 Γ— H

    where V is volume, r is radius (diameter Γ· 2), and H is height/depth.

  • Example:
    12-in diameter, 8 ft tall: Ο€ Γ— (0.5)Β² Γ— 8 = 6.28 cubic feet β‰ˆ 0.23 cubic yards.
  • Multiple columns: do one, multiply by count, then add waste to the total.

Stairs

Volume per step = run Γ— rise Γ— width. Add the steps (or use the Stairs shape above).
  • Formula:
    Vstep = Ru Γ— Ri Γ— W
    Vtotal = Vstep Γ— N

    where Ru is run (horizontal depth), Ri is rise (height), W is width, N is number of steps.

  • Example:
    5 steps, 10" run Γ— 7" rise Γ— 36" width: (10/12) Γ— (7/12) Γ— (36/12) Γ— 5 β‰ˆ 4.86 cubic feet β‰ˆ 0.18 cubic yards.
  • Stairs eat more waste, formwork and tight spaces. Use 10–15% if you're doing them by hand.

Curb and Gutter

Curb volume plus gutter volume (both are length Γ— cross-section). Add the flag if you have one.
  • Formula:
    Vcurb = L Γ— H Γ— D
    Vgutter = L Γ— W Γ— Dg
    Vtotal = Vcurb + Vgutter

    where L is length, H curb height, D curb depth, W gutter width, Dg gutter depth.

  • Example:
    50 ft: curb 6" Γ— 6" = 12.5 cu ft; gutter 12" Γ— 4" = 16.67 cu ft. Total β‰ˆ 29.2 cu ft β‰ˆ 1.08 cubic yards.
  • Residential curb often 6" Γ— 6"; gutter 12" Γ— 4". Commercial can be bigger.

Bagged vs. Ready-Mix

Bagged: 40, 60, 80 lb

Different bag sizes, different yields. Divide your cubic yards by the yield per bag and round up.
  • 40 lb:
    0.011 cubic yards (0.30 cu ft) per bag. Small repairs, under half a yard.
  • 60 lb:
    0.017 cubic yards (0.45 cu ft) per bag. Middle ground.
  • 80 lb:
    0.022 cubic yards (0.60 cu ft) per bag. Fewer bags per yard.
  • We show counts for all three once you have your volume.

Ready-Mix by Truck

Past about a yard, ready-mix usually beats bags on price and speed. No mixing, just place it.
  • Minimum:
    Most suppliers want at least 1 cubic yard. Under that, bags are the way to go.
  • Ordering:
    Order in 0.25 or 0.5 yard increments. Round up after you've added waste.
  • Check truck access and pour timing, you need a continuous pour once the truck arrives.

Weight and Transport

How Heavy Is It?

Wet concrete runs about 4,000 lbs per cubic yard (2,400 kg/mΒ³). That drives truck choice and whether your base can take the load.
  • Per cubic yard:
    ~4,000 lbs (1,814 kg).
  • Per cubic meter:
    ~2,400 kg (5,291 lbs).
  • Typical trucks carry 8–10 cubic yards. Confirm access and that forms and subgrade can support the pour.

FAQ

How much concrete do I really need?

Ordering exactly what the math says often leads to running short, subgrade irregularities, spillage, and uneven forms eat into your supply. Pros add 5–10% waste; we default to 10% and you can adjust so you finish the pour without over-ordering.

How thick should a driveway slab be?

Residential driveways: 4–6 inches. Heavier traffic or commercial use: 6–8 inches. Enter your length, width, and thickness here and we'll add waste so you get one number to order.

How many 80lb bags are in a cubic yard?

Roughly 45 bags of 80lb mix per cubic yard, each bag yields about 0.022 cubic yards (0.60 cubic feet). We show bag counts for 40lb, 60lb, and 80lb once you enter your volume.

What is the difference between bagged and ready-mix concrete?

Bagged comes in 40lb, 60lb, or 80lb bags, handy for small jobs. Ready-mix is delivered by truck with a 1-yard minimum. Past a yard, ready-mix usually wins on cost. We give you both bag counts and cubic yards so you can compare.

How do I calculate concrete for stairs?

Each step: run Γ— rise Γ— width. Example: 10" deep Γ— 7" high Γ— 36" wide β‰ˆ 0.97 cubic feet per step. Multiply by the number of steps. Use the Stairs option above and we'll do it.

What is a waste factor and why do I need it?

Waste covers spillage, over-excavation, uneven forms, and rough subgrades. Pros add 5–10%. Need 10 cubic yards? Order 11 with 10% waste. Running out mid-pour means weak cold joints and rework.

How much does concrete weigh?

Wet concrete runs about 4,000 lbs per cubic yard (2,400 kg/mΒ³). That affects truck capacity, formwork, and whether your base can support the load. We multiply your volume by that so you see estimated weight.

What is the minimum order for ready-mix concrete?

Most suppliers have a 1 cubic yard minimum. Under a yard, bags usually make more sense. We show both so you can pick the cheaper route.

DIY Estimation Note

Estimates Only: These calculators provide theoretical estimates based on standard dimensions. Material density, waste factors, and specific project conditions vary significantly.

Verify Locally: Always verify measurements and material requirements with a professional contractor or local building codes before purchasing supplies or starting work.

Project Accuracy: CalcRegistry is not responsible for material shortages, overages, or structural issues resulting from the use of these general estimates.

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