Concrete Calculator

How It Works

This calculator converts your slab dimensions into cubic yards of concrete and tells you how many premix bags you would need as an alternative. Ready-mix delivery is more economical for jobs over 1 cubic yard.

The Formula

Variables

• Length — Slab length in feet
• Width — Slab width in feet
• Depth — Slab thickness in inches (divided by 12 to convert to feet)
• 27 — Cubic feet per cubic yard
• 0.45 — Cubic feet of concrete per 60 lb bag
• 0.6 — Cubic feet of concrete per 80 lb bag

Example

A 10 ft x 10 ft slab that is 4 inches deep: volume = 10 x 10 x 0.333 = 33.3 cu ft = 1.23 cubic yards. That is 74 bags of 60 lb mix or 56 bags of 80 lb mix.

Tips

• Order 10% extra concrete to account for uneven subgrade and spillage.
• For slabs, 4 inches is the minimum depth -- use 6 inches for driveways or heavy loads.
• Ready-mix trucks usually have a minimum order of 1 cubic yard, often with a short-load fee under that.
• Concrete sets in about 24-48 hours but takes 28 days to fully cure to rated strength.
• In hot weather, mist the surface with water during the first few days to prevent cracking.