How much concrete do I need?
Measure the space, pick the shape, and enter the numbers. The calculator works out the net volume first. That is the exact geometry with nothing added. Then it applies the waste you choose to give the order volume. Both numbers stay on screen, so nothing is hidden inside one figure.
For one flat slab, the concrete slab calculator has driveway and patio presets and a gravel base estimate. If you only need yards, the concrete yard calculator covers the square feet ÷ 81 shortcut and how far a yard goes.
Concrete volume calculator: the formulas
Every shape here comes down to a few formulas. Put every measurement in feet, or convert inches by dividing by 12.
| Shape | Formula |
|---|---|
| Slab, wall, square footing | V = L × W × T |
| Round slab, column, post hole | V = π × (D ÷ 2)² × H |
| Hollow tube | V = H × π × ((D_out ÷ 2)² − (D_in ÷ 2)²) |
| Stairs (solid, on grade) | V = W × run × rise × n(n+1) ÷ 2 + landing |
| Curb and gutter | V = L × (curb W × curb H + gutter W × flag T) |
| Trapezoid | V = L × ((top + bottom) ÷ 2) × H |
The step-by-step version, with the reason behind 27 and 324, is in the concrete calculator formula guide.
Worked example: 10 × 10 ft patio, 4 in thick
- Thickness in feet: 4 ÷ 12 = 0.333 ft.
- Volume: 10 × 10 × 0.333 = 33.33 ft³.
- Cubic yards: 33.33 ÷ 27 = 1.23 yd³ (net).
- With 10% waste: 1.23 × 1.10 = 1.36 yd³ (order).
- 80 lb bags at 0.60 ft³ each: 33.33 ÷ 0.60 = 55.6, so 56 bags net, or 62 bags with 10% waste.
Assumptions: flat subgrade, no thickened edges, bag yield from the label .
Concrete estimator: from takeoff to order
A real job is rarely one rectangle. A garage might be a slab plus a thickened perimeter footing plus two pier pads. Add each piece as its own section with Add section. The calculator adds them up, applies waste once, and gives one number to order.
- Slabs and pads. Rectangle or round. For rebar, open the rebar grid panel to get bar count, linear feet, and tie points.
- Footings. Strip footings and square pads. The concrete footing calculator covers sizing questions.
- Columns and post holes. Round tube forms, with a hollow-tube option. More on the column page.
- Steps and curbs. Solid stairs on grade and a simple curb-and-gutter profile.
You can add an optional price per yard to get a rough concrete-only number. For delivery, short-load fees, and tax, use the concrete cost calculator.
How to figure concrete by hand
- Measure length, width, and depth. Measure depth in a few spots and use the average.
- Convert everything to feet. Inches ÷ 12 = feet.
- Multiply to get cubic feet.
- Divide by 27 to get cubic yards.
- Add waste if you want it, then round up to how your supplier sells.
Bags or a ready-mix truck?
Bags usually make sense for small pours, roughly under ¾ to 1 cubic yard . Past that, mixing 45 or more 80 lb bags by hand is a long, heavy day, and a truck is usually more practical. Truck minimums and short-load fees change the answer, so check with your supplier. The concrete bag calculator has the full bags-per-yard table.
Cement vs concrete
People search for a "cement calculator" when they mean concrete. Cement is the gray powder that binds everything. Concrete is cement plus sand, gravel, and water. You pour concrete. You only count cement if you are mixing from raw materials, and the concrete mix calculator splits a volume into cement, sand, and gravel.
What this calculator does not do
It estimates volume. It does not design footings, size rebar, or check local code. Thickness, reinforcement, and footing size should come from your plans, an engineer, or your building department.