Concrete Calculator
Cubic yards, bag counts, weight and cost for every pour shape — waste included, with the math shown and the yield data cited.
Your concrete pour
Concrete to order (waste included)
1.36 yd³
- 80 lb bags
- 62 bags
- Volume before waste
- 33.33 ft³
- Weight
- 5,432 lb
- Bag yields vary by brand and mix — confirm the yield printed on the bag.
How this is calculated
Raw volume
length × width × (thickness ÷ 12) × qty
= 10 × 10 × (4 ÷ 12) × 1
33.33 ft³
Add waste
raw volume × (1 + waste% ÷ 100)
= 33.33 × (1 + 10 ÷ 100)
36.67 ft³ = 1.36 yd³
80 lb bag count
ceil(volume ÷ bag yield)
= ceil(36.67 ÷ 0.6)
62 bags
Weight
yd³ × 4000 lb/yd³
= 1.36 × 4000
5,432 lb
How much concrete do I need for a 10×10 slab?
A 10 ft × 10 ft slab poured 4 inches thick contains 10 × 10 × (4 ÷ 12) = 33.3 ft³. Divide by 27 to get 1.23 cubic yards. At 0.6 ft³ per 80 lb bag that is 56 bags. Add the standard 10% slab waste and order 1.36 yd³ of ready-mix. The same math runs for every shape above — the calculator just substitutes your numbers.
Concrete bags by slab size (4 inch thick, before waste)
| Slab size | Cubic yards | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|
| 8 × 8 ft | 0.79 | 36 | 48 | 72 |
| 10 × 10 ft | 1.23 | 56 | 75 | 112 |
| 10 × 12 ft | 1.48 | 67 | 89 | 134 |
| 12 × 12 ft | 1.78 | 80 | 107 | 160 |
| 12 × 16 ft | 2.37 | 107 | 143 | 214 |
| 20 × 20 ft | 4.94 | 223 | 297 | 445 |
Concrete coverage — area one cubic yard covers
| Thickness | Coverage per yd³ |
|---|---|
| 4 inches | 81 ft² |
| 5 inches | 65 ft² |
| 6 inches | 54 ft² |
| 8 inches | 40 ft² |
Standard slab thickness by application
| Application | Typical thickness |
|---|---|
| Patio / walkway | 4 inches |
| Shed / garden slab | 4 inches |
| Driveway (cars) | 4 inches |
| Driveway (heavy vehicles) | 5–6 inches |
| Garage floor | 4–6 inches |
| Footings | 6–12 inches (per design) |
Common concrete estimating mistakes
- •Forgetting waste. Spillage, uneven subgrade and over-excavation mean you should order 5% (formed footings) to 10% (slabs) extra.
- •Rounding bags down. Always round up to whole bags — running short mid-pour ruins a monolithic finish.
- •Using nominal pi (3.14) for columns. Small errors compound across many piers; this calculator uses full-precision π.
- •Ignoring the short-load fee. Ready-mix orders under about 4 yd³ usually carry a surcharge — bagging may be cheaper for small pours.
Frequently asked questions
How much concrete do I need for a 10×10 slab?+
A 10×10 ft slab at 4 inches thick is 33.3 ft³ = 1.23 cubic yards before waste, or about 56 bags of 80 lb concrete mix. Add 10% waste and order 1.36 yd³.
How many 80 lb bags of concrete are in a cubic yard?+
There are 45 bags of 80 lb concrete mix in a cubic yard (27 ft³ ÷ 0.6 ft³ per bag). A cubic yard is 60 × 60 lb bags or 90 × 40 lb bags.
How much does a cubic yard of concrete weigh?+
Standard ready-mix concrete weighs about 4,000 lb (roughly 2 tons) per cubic yard.
How much waste should I add when ordering concrete?+
Add about 10% for slabs and 5% for formed footings. Increase it on rough or sloped ground where over-excavation fills with concrete.
Concrete calculators by pour type
Slab
Enter length, width and thickness to get the exact ready-mix yardage and bag count for a slab or pad — with waste handled and every formula shown.
OpenFooting
Size a strip or wall footing pour. Enter the length, height (depth) and thickness to get the yardage and bag count, with the lower 5% footing waste applied.
OpenColumn / Tube
Calculate concrete for round columns, deck piers and Sonotube forms. Enter the tube diameter and height to get yardage and bag count per pier.
OpenWall
Calculate a foundation or retaining wall pour from length, height and thickness — including tapered walls using the average thickness.
OpenStairs
Calculate concrete for poured steps. The calculator sums each step as a block whose height is the cumulative rise — the accurate method for stairs.
OpenCurb & Gutter
Calculate a curb-and-gutter pour from the curb and gutter dimensions and the run length, using the swept cross-sectional area.
OpenMethodology & sources
Volume is computed with the standard geometric formulas for each pour shape, carrying full precision and using exact π. Bag counts divide the waste-adjusted volume by published per-bag yields and round up to whole bags. Weight uses the conventional ready-mix density of 4,000 lb per cubic yard.
Bag yields vary by brand and mix — always confirm the yield printed on the bag. Installed-cost figures are indicative ranges; get a local quote before ordering.
- Quikrete published bag yield data (Concrete Mix No. 1101) — verified June 28, 2026
Last reviewed June 28, 2026. Estimates are indicative — verify against current product specs and local requirements before ordering.
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