How the number is worked out
cubic feet = length (ft) × width (ft) × thickness (in) ÷ 12
cubic yards = cubic feet ÷ 27
bags = cubic feet ÷ bag yield, rounded up
Thickness is the one people get wrong: it is entered in inches, so it has to be divided by 12 before it is multiplied with feet. A cubic yard is 3 ft × 3 ft × 3 ft, which is where the 27 comes from.
Bag yields we use
| Bag | Yield per bag | Bags per cubic yard |
|---|---|---|
| QUIKRETE Concrete Mix 40 lb | 0.3 ft³ | 90 |
| QUIKRETE Concrete Mix 50 lb | 0.375 ft³ | 72 |
| QUIKRETE Concrete Mix 60 lb | 0.45 ft³ | 60 |
| QUIKRETE Concrete Mix 80 lb | 0.6 ft³ | 45 |
| QUIKRETE Concrete Mix 90 lb | 0.675 ft³ | 40 |
| QUIKRETE 5000 50 lb | 0.375 ft³ | 72 |
| QUIKRETE 5000 60 lb | 0.45 ft³ | 60 |
| QUIKRETE 5000 80 lb | 0.6 ft³ | 45 |
| QUIKRETE Fast-Setting 50 lb | 0.375 ft³ | 72 |
| QUIKRETE Fast-Setting 60 lb | 0.45 ft³ | 60 |
| Sakrete 5000 Plus 50 lb | 0.38 ft³ | 72 |
| Sakrete 5000 Plus 60 lb | 0.47 ft³ | 58 |
| Sakrete 5000 Plus 80 lb | 0.6 ft³ | 45 |
| Sakrete Fast Setting 50 lb | 0.38 ft³ | 72 |
Each yield is quoted word for word from the maker's own data sheet in the sources box below. “Bags per cubic yard” is 27 divided by the yield, rounded up. The same bag weight does not always mean the same yield: a 60 lb bag of Sakrete 5000 Plus is listed at 0.47 ft³, a 60 lb bag of QUIKRETE Concrete Mix at 0.45 ft³. If your product isn't listed, read the yield on your own bag before you trust any count, including ours.
Worked example
A 10 ft × 12 ft patio poured 4 in thick:
- 10 × 12 × 4 ÷ 12 = 40 ft³
- 40 ÷ 27 = 1.48 yd³
- 80 lb QUIKRETE Concrete Mix: 40 ÷ 0.60 = 66.7 → 67 bags
- 60 lb QUIKRETE Concrete Mix: 40 ÷ 0.45 = 88.9 → 89 bags
- 60 lb Sakrete 5000 Plus: 40 ÷ 0.47 = 85.1 → 86 bags
That is before any extra for spillage or a subgrade that dips in places. The calculator leaves the extra at 0% on purpose: how much you need depends on how level your base is and how tight your forms are, and we would rather you choose it than hide an assumption inside the answer.
What this calculator is not for
It gives volume, not a design. It does not tell you how thick a slab must be for a driveway or a structure, what reinforcement to use, or what your local code requires. Irregular or sloped slabs need to be split into rectangles and added up, and a thickened edge needs its own line as a footing.
Sources
- QUIKRETE, QUIKRETE® Concrete Mix (No. 1101) — Product Data Sheet. Checked 2026-09-24.
“A 40 lb (18.1 kg) bag yields approximately 0.30 ft3 (8.5 L), a 50 lb (22.7 kg) bag yields approximately 0.375 ft3 (10.6 L), a 60 lb (27.2 kg) bag yields approximately 0.45 ft3 (12.7 L), an 80 lb (36.3 kg) bag yields approximately 0.60 ft3 (17 L) and a 90 lb (40.8 kg) bag yields approximately 0.675 ft3 (19.1 L).”
- QUIKRETE, QUIKRETE® 5000 High Early Strength Concrete Mix (No. 1007) — Product Data Sheet. Checked 2026-09-24.
“YIELD • A 50 lb (22.6 kg) bag yields approximately 0.375 ft3 (10.6 L) • A 60 lb (27.2 kg) bag yields approximately 0.45 ft3 (12.7 L) • An 80 lb (36.2 kg) bag yields approximately 0.60 ft3 (17 L)”
- QUIKRETE, QUIKRETE® Fast-Setting Concrete Mix (No. 1004) — Product Data Sheet (revised November 2025). Checked 2026-09-24.
“YIELD • Each 50 lb (22.6 kg) bag yields approximately 0.375 cu ft (10.6 L) • Each 60 lb (27.2 kg) bag yields approximately 0.45 cu ft (12.7 L) … Start by digging the post hole about 3 times the diameter of the post. Hole depth should be 1/3 the overall post height.”
- Sakrete, Sakrete 5000 Plus High Early Strength Concrete Mix — Technical Data Sheet. Checked 2026-09-24.
“PACKAGE SIZE YIELD WATER REQUIRED SLUMP RANGE 50 lb 22.7 kg 0.38 ft3 0.011 m3 2.1 qts 2.0 L 2 – 3 in 50 – 75 mm 60 lb 27.2 kg 0.47 ft3 0.013 m3 2.5 qts 2.4 L 2 – 3 in 50 – 75 mm 80 lb 36.3 kg 0.6 ft3 0.017 m3 3.5 qts 3.3 L 2 – 3 in 50 – 75 mm … A general rule of thumb is that the depth should be 1/3 the length of the post or pole and the diameter should be 3 times that of the pole or post”
- Sakrete, Sakrete Fast Setting Concrete Mix — Technical Data Sheet. Checked 2026-09-24.
“Post Setting - Based on Average 10” Diameter Hole: … Bag Size Yield Water 50 lb (22.6 kg) 0.38 ft3 (.01 m3) 2.5 to 3 qts (2.4 - 2.9 L) 12” (305 mm) deep 18” (457 mm) deep 1.25 bags 2 bags 24” (610 mm) deep 30” (762 mm) deep 2.5 bags 3 bags”
- QUIKRETE, QUIKRETE® Quantity Calculator. Checked 2026-09-24.
“All yields are approximate and do not include allowance for uneven subgrade, waste, etc.”
- Sakrete, Sakrete Calculators. Checked 2026-09-24.
“PRO TIP: Remember to add 10% to your estimates for safety!”
- NIST, NIST Handbook 44 (2026), Appendix C — General Tables of Units of Measurement. Checked 2026-09-24.
“1 728 cubic inches (in3) = 1 cubic foot (ft3) 27 cubic feet = 1 cubic yard (yd3)”