How much concrete do I need? Yards, bags and when to order a truck
Multiply length by width by thickness, divide by 27 for cubic yards and add 5 to 10% extra. A cubic yard takes 45 bags of 80 lb, 60 of 60 lb or 90 of 40 lb. Under about a yard, bags make sense; at two yards or more, order a truck.
Most patios and walkways are poured 4 inches thick and driveways 5 to 6 inches; check your local code. At 4 inches, one cubic yard covers 81 square feet.
Worked example
Example: a 12 × 10 ft slab, 4 inches thick, with 5% extra and 80-lb bags that make 0.6 cubic feet each.
This example gives 1.56 cubic yards of concrete.
- 12 × 10 × 0.3333 = 40 cu ft per rectangle
- 40 × 1 identical shapes = 40 cu ft
- 40 × (1 + 5/100) ÷ 27 = 1.5556 cu yd
- Edge forms: 2 × (12 + 10) = 44 ft
Other calculators for this job
Every step of a concrete project: measure, the list, what it costs and the quotes.
Bags per cubic yard
One cubic yard is 27 cubic feet. The bag counts use QUIKRETE 1101’s stated yields and are rounded up to whole bags; the last column is this guide’s 12 × 10 ft slab, 4 inches thick (40 cubic feet), before any extra.
| Bag | Makes | Bags per cubic yard | 12 × 10 ft slab, 4 in |
|---|---|---|---|
| 80 lb | 0.60 cu ft | 45 | 67 bags |
| 60 lb | 0.45 cu ft | 60 | 89 bags |
| 40 lb | 0.30 cu ft | 90 | 134 bags |
What changes the order?
The same slab at greater thickness takes more concrete: at 6 inches it needs half as much again as at 4.
| Calculator input | Result from those inputs |
|---|---|
| Thickness (in): 3 | 1.17 cubic yards of concrete |
| Thickness (in): 4 | 1.56 cubic yards of concrete |
| Thickness (in): 6 | 2.33 cubic yards of concrete |
Try your own measurements in the concrete calculator.
Measure each shape once
Split the pour into rectangles, circles and steps that do not overlap: a slab with a thicker edge is a slab plus a footing strip. Measure length and width in feet and thickness in inches. A 12 × 10 ft slab at 4 inches is 12 × 10 × 4 ÷ 12 = 40 cubic feet, or 1.48 cubic yards.
Add extra, then round up
Order 5 to 10% more than you measured: forms bow, the ground dips, and running short mid-pour leaves a weak seam. Round up to whole bags. Ready-mix plants sell in set steps and have a minimum load, so ask for both when you call.
Bags or a truck
An 80-lb bag makes about 0.6 cubic feet, so a cubic yard takes 45 bags weighing 3,600 lb. Under about a yard, bags are practical; at two yards or more a truck saves hours of mixing. Plants charge extra for small loads, so ask for that fee with the price per yard. Check the payload on the sticker in your truck’s door frame: a pickup rated for 1,600 lb carries 20 bags of 80 lb.
Before the truck comes
Tell the plant where the truck can park and how far the concrete has to travel; a pump or a line of wheelbarrows costs time and money. Ask how long the driver waits before charging and what happens to concrete left over. Reinforcement, the gravel base and curing follow your plan or local code.