Concrete Calculator

Common Questions

How much concrete do I need for a 10×10 slab?

For a 10′ × 10′ slab at 4″ thick with a 10% waste margin: 1.36 cubic yards (62 × 80lb bags or 82 × 60lb bags). Without the waste margin, the raw volume is 1.23 cubic yards (56 × 80lb / 74 × 60lb). Use the Slab mode below to compute your exact dimensions in imperial or metric.

Why does the calculator add a waste margin?

Concrete losses (spillage, over-trowel, formwork imperfections) typically run 5–15%. A 10% margin is the construction-industry default. If your forms are tight you can drop it to 5%; if conditions are difficult, bump to 15%.

How many cubic feet are in a cubic yard?

Exactly 27. A cubic yard is 3 × 3 × 3 feet. In metric, 1 cubic yard ≈ 0.7646 m³.

How many 80lb bags of concrete are in a cubic yard?

About 45. Each 80lb bag yields 0.60 ft³, so 27 ÷ 0.60 = 45 bags per cubic yard.

How much concrete does a 25kg bag yield?

About 11.7 litres (0.0117 m³). A 20kg bag yields about 9.4 litres. So 1 m³ of concrete needs roughly 86 × 25kg bags or 107 × 20kg bags.