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Concrete calculator: yards, bags and trucks for any pour
Cubic yards are length × width × thickness in feet, divided by 27. Add every slab, footing, wall and pier on the job below, set a waste factor, and get the ready-mix order, the bag count and the number of trucks in one place.
Pours
Pour 1 — 2.96 CY before waste
What to order
Cubic yards with waste
3.26
2.96 CY net, 80 cu ft
Ready-mix order
3.5 CY
Rounded up to the quarter yard
80-lb bags
147
or 196 × 60-lb, 294 × 40-lb
Trucks (10 CY)
1
Confirm your plant's drum size
Under about 4 yards, many plants add a short-load fee on small orders — ask before you schedule. Below roughly a yard, premixed bags are often simpler than a truck.
Quantities are half a bid. Send these to the free estimate builder to add labor, burden and markup, then hand the customer a proposal.
Every field takes arithmetic — type 24+18+12 and it adds. Nothing is sent anywhere; the math runs in your browser.
How to calculate concrete in cubic yards
Convert every dimension to feet — thickness in inches divided by 12 — multiply, then divide by 27. A 20 × 12 ft patio at 4 inches: 20 × 12 × 0.333 = 80 cubic feet ÷ 27 = 2.96 cubic yards. With 10% waste that is 3.26 yards, and because ready-mix is sold in quarter yards, you order 3.5.
Footings work the same way with the cross-section in inches: 40 ft of 16 × 8 inch footing is 40 × 1.333 × 0.667 = 35.6 cubic feet, 1.32 yards. Round piers use π × radius² × height, so a 12-inch sonotube 4 ft deep holds 3.14 cubic feet — small alone, but twenty of them is 2.3 yards.
How much a yard of concrete covers
| Slab thickness | Sq ft per cubic yard | Yards per 1,000 sq ft |
|---|---|---|
| 3" | 108 | 9.26 |
| 3.5" | 92.6 | 10.8 |
| 4" | 81 | 12.35 |
| 5" | 64.8 | 15.43 |
| 6" | 54 | 18.52 |
| 8" | 40.5 | 24.69 |
Figures are net. Add your waste factor before ordering.
Bags of premixed concrete per yard
| Bag size | Typical yield | Bags per cubic yard |
|---|---|---|
| 80 lb | 0.60 cu ft | 45 |
| 60 lb | 0.45 cu ft | 60 |
| 40 lb | 0.30 cu ft | 90 |
Yields are the typical figures printed on premixed bags; check the brand you buy. The same 20 × 12 patio is about 147 80-lb bags with waste — which is why anything past a yard or two usually goes to a truck.
From yardage to a bid
Yardage is the easy part of a concrete number. Forms, base, vapor barrier, reinforcement, pump time and finish labor are where bids are won or lost — price the pour, not just the yardage. Stone base under the slab comes from the gravel calculator, block stem walls from the concrete block calculator, and the finished quantities drop straight into the free estimate builder.
Frequently asked questions
How do I calculate how much concrete I need?
Multiply length by width by thickness, all in feet, and divide by 27 to get cubic yards. A 20 × 12 ft slab at 4 inches is 20 × 12 × 0.333 = 80 cubic feet, or 2.96 yards. Add 5–10% for subgrade variation and spillage and order 3.25 to 3.5 yards.
How many bags of concrete are in a yard?
About 45 80-lb bags, 60 60-lb bags, or 90 40-lb bags, using the typical published yields of 0.60, 0.45 and 0.30 cubic feet per bag. Yields vary slightly by brand and mix, so check the bag before you buy for a large pour.
How many square feet does a yard of concrete cover?
81 square feet at 4 inches thick, 54 at 6 inches, and 108 at 3 inches. The rule is 324 divided by the thickness in inches. That number is before waste, so a 4-inch slab of 810 sq ft needs 10 yards net and about 11 on the order.
How much extra concrete should I order?
Most contractors add 5–10%. A subgrade that averages half an inch low turns a 4-inch slab into 4.5 inches — 12.5% more concrete — so rough or unproofed grade deserves the high end. Running short mid-pour means a cold joint or a second short-load truck, both of which cost more than the extra quarter yard.
Is it cheaper to use bags or ready-mix?
Under roughly a yard, bags are usually simpler; a single yard is already 45 80-lb bags to mix by hand or in a small mixer. Past a yard or two, ready-mix normally wins on labor and consistency even with a short-load fee. Get your plant's minimum and short-load charge before deciding.
Quantities are half the bid.
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