Concrete Calculator

Estimate cubic yards and bags for slabs, columns, and footings.

Shape

Dimensions in

Length

Width

Thickness

How to Use This Calculator

1. Select the shape of your pour (slab, column, or footing).

2. Enter dimensions — you can work in feet or inches.

3. Read off cubic yards for ready-mix ordering, or bag counts for DIY bags.

Pro tip: Always order 5–10% extra to account for spillage and uneven subgrades.

4" driveway slab, 20×20 ft: 20 × 20 × 0.333 ft ÷ 27 = 4.9 cubic yards

8" round column, 10 ft tall (12" dia): π × 0.5² × 10 ÷ 27 = 0.29 cubic yards

12"×12" footing, 2 ft deep: 1 × 1 × 2 ÷ 27 = 0.07 cubic yards

How many bags per cubic yard?

A 60 lb bag yields ~0.45 cu ft; an 80 lb bag ~0.6 cu ft. You need 27 cu ft per cubic yard — roughly 60 × 60 lb bags or 45 × 80 lb bags.

What PSI should I order?

Driveways: 4,000 PSI. Walkways/patios: 3,000 PSI. Structural footings: 4,000–5,000 PSI.

Is ready-mix cheaper than bags?

Generally yes for pours over 1 cubic yard. Ready-mix runs $125–$200/cu yd depending on your region; bags cost the equivalent of $250–$350/cu yd.

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