Concrete Calculator
Calculate how much concrete you need for slabs, footings, post holes, columns, and steps. Get cubic yards, cubic feet, cubic meters, and bag counts.
What is a concrete calculator?
A concrete calculator estimates the volume of concrete needed from your pour’s dimensions, then converts that volume into the units you buy or order—such as cubic yards, cubic feet, cubic meters, and concrete bags.
How much concrete do I need?
The amount depends on footprint, thickness or depth, shape, how many identical pours you have, and any optional waste allowance. Example: 10 × 10 ft × 4 in = 33.33 ft³ = 1.23 yd³ before waste.
How to use the concrete calculator
- Choose the pour shape.
- Select imperial or metric units.
- Enter the dimensions and quantity.
- Add another pour if the project has more than one shape.
- Add optional waste, a custom bag yield, or prices.
- Read cubic feet, cubic yards, cubic meters, and 40/60/80 lb bag counts.
- Copy, share, or print the estimate.
Concrete volume formula
- Rectangle: volume = length × width × depth (same units first)
- Imperial: depth(ft) = depth(in) ÷ 12; yd³ = ft³ ÷ 27
- Metric: m³ = L(m) × W(m) × D(m); 1 m³ = 35.3146667 ft³
- Cylinder: π × r² × height
- Solid stairs (this tool): width × (n × tread) × (n × riser) ÷ 2
- Order volume = base × (1 + waste%) when waste is on
How many bags of concrete do I need?
Bags = CEILING(adjusted cubic feet ÷ bag yield). Nominal yields used here: 40 lb ≈ 0.30 ft³, 60 lb ≈ 0.45 ft³, 80 lb ≈ 0.60 ft³. Those are not universal. Check the label. Example: 33.33 ft³ ÷ 0.45 ≈ 74.07 → 75 bags.
1 cubic yard = 27 cubic feet, so 33.33 ÷ 27 ≈ 1.23 yd³ for ready-mix.
Concrete calculator for slabs and patios
Use length × width × thickness. A 10 × 10 ft pad 4 in thick is 100 ft², 33.33 ft³, 1.23 yd³. At 4 in, 1 yd³ covers 81 ft²; at 6 in, 54 ft²; at 8 in, 40.5 ft². Those are volume relationships, not required thicknesses. Use the finished thickness from your plans or local requirements.
Concrete calculator for footings
Enter total run length, width, and depth. This estimates volume only. It does not size the footing, check soil bearing, frost depth, reinforcement, or code compliance.
Concrete calculator for post holes and columns
Post holes and round columns use πr²h. A 12 in diameter × 24 in deep hole is 1.57 ft³ (0.058 yd³). Fifteen of those holes are 23.56 ft³. Need post spacing first? Use the Fence Calculator.
Concrete calculator for steps
Step mode assumes a solid triangular fill under the nosings: width × total run × total rise ÷ 2. It is not a full architectural stair takeoff. If your stairs are open treads or a custom stringer, treat this as a first estimate only.
Real concrete calculation examples
- 10×10 patio, 4 in: 1.23 yd³ before waste.
- 12×20 slab, 6 in: 4.44 yd³ before waste.
- 15 post holes, 12×24 in: 0.87 yd³ before waste.
- 20 m × 10 m × 10 cm: 20 m³.
- 80 ft² sidewalk, 4 in: 0.99 yd³.
Ready-mix vs bagged concrete
Bags are convenient for small pours and need mixing. Ready-mix is often practical for larger continuous pours, but supplier minimums and delivery matter. Neither is always cheaper. Optional prices here are material estimates only.
Common mistakes
- Mixing inches and feet without converting.
- Using area without multiplying by thickness.
- Confusing cubic feet with square feet.
- Forgetting quantity on repeated holes or pads.
- Counting bags from bag weight instead of labeled yield.
- Rounding yards first, then calculating bags.
- Treating waste as required volume.
- Assuming one bag yield for every brand.
- Using this tool to pick structural thickness.
- Ignoring ready-mix minimums and delivery rules.
How results are calculated
Volume math is deterministic. Bag counts use the exact adjusted cubic feet, then round up. Calculations run in your browser and your project measurements are not uploaded to EverydayTools servers. Share links store values in the URL hash only. This page does not determine slab thickness, PSI, rebar, frost depth, or code compliance.
Frequently asked questions
How much concrete do I need?
You need the pour volume: area × thickness for a slab, or πr²h for a hole or column. A 10×10 ft slab 4 in thick is 1.23 yd³ before waste.
How do you calculate cubic yards of concrete?
Convert all dimensions to feet, multiply length × width × depth for cubic feet, then divide by 27.
How many bags of concrete do I need?
Divide the adjusted cubic feet by the bag’s labeled yield and round up. 33.33 ft³ ÷ 0.45 ft³ → 75 of the 60 lb bags used as a nominal example.
How many 80 lb bags of concrete do I need?
Using a nominal 0.60 ft³ yield, 33.33 ft³ needs 56 bags. Check the bag — yield is not the same as weight.
How many 60 lb bags of concrete do I need?
Using a nominal 0.45 ft³ yield, 33.33 ft³ needs 75 bags. Confirm the label.
How many 40 lb bags of concrete do I need?
Using a nominal 0.30 ft³ yield, 33.33 ft³ needs 112 bags.
How much concrete do I need for a 10×10 slab?
At 4 in: 1.23 yd³ (33.33 ft³) before waste. Change the thickness if your plans specify something else.
How do I calculate concrete for a footing?
Enter run length, width, and depth. The tool multiplies those three. It does not choose the footing size.
How do I calculate concrete for post holes?
Use diameter, depth, and the number of holes. Volume per hole is πr²h, then multiply by quantity.
How do I calculate concrete for a round column?
Same cylinder math as a post hole: diameter, height, and how many columns.
What is the difference between cubic feet and cubic yards?
A cubic yard is 27 cubic feet. Ready-mix is usually quoted in yards; bag math is usually in cubic feet.
Should I add extra concrete for waste?
Often yes on uneven subgrade or sloppy forms — but it is optional here. Typical allowances are 5–15%. There is no universal 10%.
Can I calculate concrete in metric units?
Yes. Switch to meters and centimeters for cubic meters and liters.
Does the calculator estimate structural slab thickness?
No. Enter the thickness from your plans, engineer, contractor, or local requirements. This tool only multiplies the numbers you provide.
Is the calculator browser-based?
Yes. Measurements stay on your device. Share links use the URL hash only.
Related construction calculators
- Gravel Calculator — Base or subgrade gravel under a slab — not the concrete volume.
- Fence Calculator — Post and panel counts before you size post-hole concrete.
- Paver Calculator — Paver count for a patio surface, not the concrete pour.
- Topsoil Calculator — Soil volume around the pour, not concrete.
- Mulch Calculator — Landscape mulch after forms come off.
- Sand Calculator — Bedding sand for pavers beside a concrete pad.
Need the gravel base under the slab? Use the Gravel Calculator. Planning pavers around the pad? Use the Paver Calculator.