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.
Walkways are poured at least 4 inches thick and patios 3 1/2 to 4 inches; city rules for driveways set a minimum, 4 inches in some towns and 6 in others. 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 |
| 50 lb | 0.375 cu ft | 72 | 107 bags |
| 40 lb | 0.30 cu ft | 90 | 134 bags |
How thick? Concrete by project
Thickness changes the order a lot: at 4 inches a cubic yard covers 81 sq ft, at 6 inches only 54. The plan for your job and your building department have the final word.
| Project | Thickness | Source | A cubic yard covers |
|---|---|---|---|
| Sidewalk or path | At least 4 in | QUIKRETE’s sidewalk instructions | 81 sq ft |
| Patio | 3 1/2 to 4 in, on about 4 in of compacted gravel | QUIKRETE’s patio and slab instructions: 2 × 4 forms make a 3 1/2 in slab | 81 to 93 sq ft |
| Shed base or other small slab | 4 to 6 in, by the load it bears | QUIKRETE’s small-slab instructions | 54 to 81 sq ft |
| Floor slab in a house | At least 3 1/2 in; below grade, on a 4 in base of sand or gravel unless the soil drains well | International Residential Code, R506 | 93 sq ft |
| Driveway | At least 4 to 6 in, as your city sets it | City rules differ: at least 4 in over 4 in of gravel in Des Plaines, Illinois; at least 4 in in Newark, Delaware; at least 6 in with welded wire in Davison, Michigan | 54 to 81 sq ft |
Which bag mix?
Every one of these makes the same volume for the same bag weight: 0.60 cu ft for 80 lb, 0.45 for 60 lb, 0.375 for 50 lb and 0.30 for 40 lb, so the bag count above holds for any of them. The strength your slab or footing needs comes from your plan or your local code.
| Mix | Strength at 28 days | Sooner | What it is for | Bags |
|---|---|---|---|---|
| Concrete Mix (No. 1101) | 4,000 psi | 2,500 psi at 7 days | The everyday mix for slabs, footings, steps, walks and post footings, 2 in thick or more | 40, 50, 60 and 80 lb |
| 5000 High Early Strength (No. 1007) | 5,000 psi | 1,500 psi at 1 day; walk on it after 10 to 12 hours | Gains strength fast, which suits cold weather and a slab you need back soon | 50, 60 and 80 lb |
| Crack Resistant (No. 1006) | 4,000 psi | 2,500 psi at 7 days | Synthetic fibers for less shrinkage cracking, and air entrained to stand up to freezing and thawing | 50, 60 and 80 lb |
| Fast-Setting (No. 1004) | 4,000 psi | Sets in 20 to 40 minutes; 1,000 psi at 24 hours | Poured dry into a post hole and soaked: two 50 lb bags set a 3 in post in a 9 in hole 30 in deep. Wait 4 hours before loading the post or walking on a slab | 50 and 60 lb |
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. It is the combined weight of the people and the cargo, so take off yourself, any passengers and anything else on board first: a pickup rated for 1,600 lb with a 200 lb driver has 1,400 lb left, which is 17 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.