Weight concrete calculator
What the finished pour weighs, for hauling and for the forms.
Decimals fine. Bag counts round up.
At 20 × 20 ft and 4 inches you need
4.94 cubic yards
133.3 cubic feet · 18,670 lb of concrete · order 5.43 yd³ with the 10% waste allowance
Order ready-mix. At 4.94 yd³ you are 3.7 times past the point where bagging pays. That is one truck, one morning — against 223 bags to lift, mix and place before the first batch sets.
Two rules, each where it applies. Bag counts carry no waste allowance — a partial bag is not a thing you can buy, and an unopened one goes back — so the headline count is the volume and the figure beside it is the same count with waste. The ready-mix figure carries its allowance inside because a truck will not come back for a quarter yard.
The inch that costs $240
Thickness runs from the top of the compacted gravel to the finished surface. Measure from the dirt and you count the base as concrete: on this pour, one inch of that error is 1.23 extra cubic yards — about $240 of ready-mix, or 56 bags nobody needed. Set a stake to the finished height before you order.
The arithmetic, in the open
How this page gets its numbers
- Volume, cubic feet
- 20 × 20 × (4 ÷ 12) = 133.3 ft³
- Cubic yards
- 133.3 ft³ ÷ 27 = 4.94 yd³
- 80 lb bags
- ceiling(133.3 ÷ 0.60 ft³ a bag) = 223 bags, no waste allowance; with 10% waste, 245
- 60 lb bags
- ceiling(133.3 ÷ 0.45 ft³ a bag) = 297 bags, no waste allowance; with 10% waste, 326
- Weight
- 133.3 ft³ × 140 lb per ft³ = 18,670 lb
- Order allowance
- 4.94 yd³ plus 10% = 5.43 yd³ ordered
- Truck loads
- ceiling(5.43 yd³ ordered ÷ 10 yd³ a load) = 1 — a full truckload is typically about 10 cubic yards
Bag counts round up. A partial bag is not a thing you can buy, so a calculated 222.2 bags is 223 bags.
Weight presets
The 6 sets people ask for most
| Slab | Area ft² | Cubic yards | 80 lb bags→ with 10% waste | Buy as |
|---|---|---|---|---|
| 20 × 20 ft, 4 in | 400 | 4.94 | 223→245 | Ready-mix |
| 20 × 20 ft, 5 in | 400 | 6.17 | 278→306 | Ready-mix |
| 20 × 20 ft, 6 in | 400 | 7.41 | 334→367 | Ready-mix |
| 20 × 20 ft, 8 in | 400 | 9.88 | 445→489 | Ready-mix |
| 24 × 24 ft, 4 in | 576 | 7.11 | 320→352 | Ready-mix |
| 24 × 24 ft, 6 in | 576 | 10.67 | 480→528 | Ready-mix |
A different shape
The other 7 calculators
Asked about this shape
Questions
What does that pour weigh?
About 18,670 lb, at 140 lb per cubic foot. That is the figure to check against a trailer, a hoist or a suspended form, not against the truck: the plant carries its own load.
What is the weight figure for?
Hauling. Concrete runs about 140 lb per cubic foot, so a cubic yard weighs roughly 3,780 lb. Anything above half a yard is past what a half-ton pickup should carry, which is another reason the bag route stops making sense long before the arithmetic does.
Why 140 lb per cubic foot?
It is the unit weight on the bag manufacturer's own data sheet, measured to ASTM C138. Delivered ready-mix is commonly heavier than a bagged mix; rather than quote two uncited numbers this site uses the one cited number everywhere. Lightweight and heavyweight mixes exist and it does not model them.
How much concrete does 20 × 20 ft and 4 inches take?
4.94 cubic yards, which is 133.3 cubic feet before any allowance. Order 5.43 yd³ to carry the 10% waste.
What is a mixer-truck load?
A full truckload is typically about 10 cubic yards, and that is the figure this site plans with. Ask when you book: drums vary, and a plant will tell you what it is sending. The load count here is worked from the ordered volume — the one that already includes the 10% allowance — because that is what actually has to fit on the truck.
How much extra should I order?
10 percent, and where it appears depends on what you are buying. Ready-mix carries it inside the ordered figure, because a truck will not come back for a quarter yard. Bag counts do not: the headline count is the volume, and the plus figure sits beside it, because bags are bought one at a time and an unopened one goes back. Either way the allowance covers spillage, a base that is not perfectly flat and the thickness you gain at the edges of the form.
Does this include rebar, forms or labour?
No. The price band is concrete delivered: your own price per yard on the ordered volume, taken 15% either side of the middle to cover what a quote actually varies by. Forms, gravel, mesh or bar, a pump if the truck cannot reach, and finishing are all separate. Get the plant to quote your postcode before you budget.
Bag yields: QUIKRETE Concrete Mix data sheet No. 1101. Price basis: Concrete Financial Insights weighted average selling price for 2025, escalated with U.S. Bureau of Labor Statistics PPI series PCU327320327320 (2026-07). Prices vary by region — enter your own quote above.
Updated 2026-08-25