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Concrete Calculator

Pick a shape and enter its dimensions; results update as you type. Switch between imperial and metric and adjust waste, bag size, mix ratio and prices.

Local calculation · inputs stay in your browser

Inputs

Results

    An input link contains the values you entered. Share only information you want to disclose.

    Shapes and dimensions

    Slab, patio or footing

    WLT
    Volume = L × W × T. Driveways are usually 4–6 in (10–15 cm) thick; for a footing, T is the depth.

    Round column, post hole or tube

    DHdD
    Column = π/4 × D² × H; tube = π/4 × (D² − d²) × H. For a post hole you can subtract the square post that sits in the concrete.

    Solid concrete steps

    drL12n
    Step i is i risers (r) tall and one run (d) deep: V = width × d × r × n(n+1)/2, plus width × L × n × r for a top landing of depth L.

    Curb and gutter cross-section

    chgt
    V = (c × (h + t) + g × t) × length, where c = curb depth, h = curb height, g = gutter width and t = flag thickness.

    Concrete bag yield chart

    Yield per bag and bags per cubic yard or cubic metre (before waste); the last column is the area one bag covers at 4 in thick.

    Concrete bag yield chart
    Bag sizeft³ per bagLitres per bagBags per yd³Bags per m³ft² covered at 4 in
    80 lb0.617.045.058.91.8
    60 lb0.4512.760.078.51.35
    50 lb0.37510.672.094.21.12
    40 lb0.38.590.0117.70.9
    40 kg0.66118.740.853.41.98
    30 kg0.49614.054.471.21.49
    25 kg0.41311.765.385.41.24
    20 kg0.3319.481.6106.80.99

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    Formula and method

    Slab/footing V = L×W×T; wall V = L×H×T; round column V = π/4×D²×H (minus a²×H for a post); square column V = A×B×H; tube V = π/4×(D²−d²)×H; circular slab V = π/4×D²×T; steps V = W×run×rise×n(n+1)/2 + W×landing×n×rise; curb V = L×[c×(h+f)+g×f]. Order = V × quantity × (1 + waste). 1 yd³ = 27 ft³ = 0.764555 m³. Bags = ceil(order ÷ yield per bag). Site mix: dry volume = 1.54 × wet volume, cement at a bulk density of 1440 kg/m³.

    Worked example

    A 10 ft × 10 ft slab, 4 in thick: 10 × 10 × (4/12) = 33.33 ft³ = 1.235 yd³ (0.944 m³). With no waste that is 56 bags of 80 lb (0.60 ft³ each) and about 5,000 lb of wet concrete. With 5% waste, order 1.30 yd³ or 59 bags.

    Assumptions and limits

    • Bag yields are the values printed on common US premix bags (80 lb ≈ 0.60 ft³); metric bags use the same yield per kilogram (25 kg ≈ 11.7 L). Brands differ slightly, so check the bag.
    • A 5–10% waste allowance covers uneven subgrade, form bulge and spillage; use more on rough ground.
    • Site-mix ratios are by volume; the 1.54 dry factor and 0.5 water-cement ratio are estimates. Structural members need a designed mix for the required strength and local code.
    • Results exclude rebar, gravel base and formwork; use the rebar weight calculator for steel.

    Frequently asked questions

    How many bags of concrete are in a yard?

    1 yd³ = 27 ft³: about 45 bags of 80 lb, 60 bags of 60 lb or 90 bags of 40 lb before waste. One cubic metre takes about 85 bags of 25 kg.

    Should I use bags or order ready-mix?

    Bags are practical below about 1 yd³ (0.75 m³). Above that, hand mixing becomes heavy work and ready-mix is often cheaper and more consistent. Enter both prices to compare.

    How thick should a concrete slab be?

    Walkways and patios are commonly 4 in (10 cm), home driveways 4–6 in (10–15 cm); heavy-duty areas need an engineered design.

    How much does a cubic metre of concrete weigh?

    Normal-weight concrete is about 2,400 kg/m³ (150 lb/ft³, about 4,050 lb/yd³); reinforced about 2,500 kg/m³; lightweight about 1,840 kg/m³.

    References

    Concrete Calculator practical guide and common questions

    What does Concrete Calculator calculate?

    Pick a shape and enter its dimensions; results update as you type. Switch between imperial and metric and adjust waste, bag size, mix ratio and prices. Slab/footing V = L×W×T; wall V = L×H×T; round column V = π/4×D²×H (minus a²×H for a post); square column V = A×B×H; tube V = π/4×(D²−d²)×H; circular slab V = π/4×D²×T; steps V = W×run×rise×n(n+1)/2 + W×landing×n×rise; curb V = L×[c×(h+f)+g×f]. Order = V × quantity × (1 + waste). 1 yd³ = 27 ft³ = 0.764555 m³. Bags = ceil(order ÷ yield per bag). Site mix: dry volume = 1.54 × wet volume, cement at a bulk density of 1440 kg/m³.

    When is this useful?

    A 10 ft × 10 ft slab, 4 in thick: 10 × 10 × (4/12) = 33.33 ft³ = 1.235 yd³ (0.944 m³). With no waste that is 56 bags of 80 lb (0.60 ft³ each) and about 5,000 lb of wet concrete. With 5% waste, order 1.30 yd³ or 59 bags.

    How do I enter the inputs?

    Enter the inputs for Concrete Calculator: Shape, Units, Length, Width, Thickness or depth, Height or depth, Diameter D, Inner diameter d, Square post to subtract (optional), Side A, Side B, Slab diameter, Rise per step, Run per step, Number of steps, Top landing depth (optional), Curb depth (top width), Curb height above gutter, Gutter width, Flag (gutter) thickness, Quantity (identical pours), Waste allowance, Premix bag size, Yield per bag, Concrete type (for weight), Site-mix ratio (optional), Price per bag (optional), Ready-mix price (optional). Calculate, check the units and assumptions, then copy or download the results.

    How should I interpret the results?

    Bag yields are the values printed on common US premix bags (80 lb ≈ 0.60 ft³); metric bags use the same yield per kilogram (25 kg ≈ 11.7 L). Brands differ slightly, so check the bag. A 5–10% waste allowance covers uneven subgrade, form bulge and spillage; use more on rough ground. Site-mix ratios are by volume; the 1.54 dry factor and 0.5 water-cement ratio are estimates. Structural members need a designed mix for the required strength and local code. Results exclude rebar, gravel base and formwork; use the rebar weight calculator for steel.

    Where are my inputs processed?

    Concrete Calculator runs in this browser. Inputs are not uploaded to a calculation server; copying and CSV download require your action. The existing site analytics and advertising still load.