Concrete Calculator (Slab Volume & Bags)
Concrete calculator: volume of a slab, patio or footing in cubic yards or m³, with 10 % extra and the number of premix bags.
V = L · W · T
How to use this calculator
- Choose the quantity you want under “Solve for”.
- Type the known values and pick their units: any combination works.
- The result updates as you type. Open “Show the steps” to see the substitution.
Volume = length × width × thickness. Order 5–10 % extra for spillage and uneven ground.
An 80 lb bag yields about 0.6 ft³; 27 ft³ make one cubic yard.
Formula
V = L · W · T
| Symbol | Quantity | Units |
|---|---|---|
| L | Length | m, km, cm, mm, µm, nm, pm, Å, in, ft, yd, mi, nmi, au, ly |
| W | Width | m, km, cm, mm, µm, nm, pm, Å, in, ft, yd, mi, nmi, au, ly |
| T | Thickness | m, km, cm, mm, µm, nm, pm, Å, in, ft, yd, mi, nmi, au, ly |
| V | Concrete volume | L, mL, µL, m³, dm³, cm³, gal, gal (UK), qt, pt, cup, fl oz, ft³, yd³, in³ |
Worked example
Given: L = 9.84252 ft · W = 9.84252 ft · T = 3.93701 in
V = L W T
Result: V = 1.17716 yd³
Concrete volume for different values of Length
| L · Length | V · Concrete volume |
|---|---|
| 4.921 ft | 0.58858 yd³ |
| 7.382 ft | 0.88287 yd³ |
| 8.858 ft | 1.0594 yd³ |
| 9.843 ft | 1.1772 yd³ |
| 10.83 ft | 1.2949 yd³ |
| 12.3 ft | 1.4714 yd³ |
| 14.76 ft | 1.7657 yd³ |
| 19.69 ft | 2.3543 yd³ |
Other values as in the worked example.
Frequently asked questions
Concrete for a 10 × 10 ft slab, 4 in thick?
About 1.23 yd³, or 62 bags of 80 lb including 10 % extra.
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