AreaMapConcrete calculator
Enter the slab’s length, width and thickness. The calculator adds extra for spillage and uneven ground and gives cubic yards of ready-mix and bags.
How concrete is calculated
Length × width × thickness in feet (inches ÷ 12) gives cubic feet; divide by 27 for cubic yards. Add 5 to 10% for spillage and an uneven base. Bags are sold by weight: an 80 lb bag makes about 0.6 ft³, a 60 lb bag 0.45 ft³ and a 40 lb bag 0.3 ft³.
Example: a 10 × 10 ft patio 4 in thick is 33.3 ft³, or 1.23 yd³. With 10% extra that’s 1.36 yd³, or 62 bags of 80 lb.
How thick should a slab be?
| Project | Thickness |
|---|---|
| Sidewalks, patios, shed floors | 4 in |
| Driveways | 4 to 5 in for cars, 6 in for trucks |
| Garage floors | 4 to 6 in |
| Equipment pads | 6 in or more |
Above about one cubic yard, ready-mix delivery is usually cheaper and much less work than mixing bags. For odd-shaped slabs and driveways, trace the outline in AreaMap: it gives the area and the concrete, rebar and mesh for the job.
Questions
How many bags of concrete are in a yard?
About 45 bags of 80 lb, 60 bags of 60 lb or 90 bags of 40 lb.
How thick should a concrete patio be?
4 in is standard for patios and walkways. Go to 5 or 6 in where vehicles drive.
When should I order ready-mix instead of bags?
Usually above one cubic yard. A 10 × 10 ft slab 4 in thick already takes over 60 bags of 80 lb.
How much extra concrete should I order?
5 to 10%. Running short in the middle of a pour is much worse than a little left over.