Concrete Calculator
Planning a concrete project? Calculate exactly how much material you need. Enter the dimensions of your slab, footing, or post holes to get the cubic metres of ready-mix concrete or number of bags required. Includes waste factor for accurate ordering.
Reviewed by the SparkCalc editorial team
How We Calculate This
Volume = Length x Width x (Depth/12) in cubic feet. Divide by 27 for cubic yards. 80 lb bag yields 0.6 cu ft. 60 lb bag yields 0.45 cu ft. Waste factor added to total.
Sources: American Cement Association (formerly Portland Cement Association) — Cement & Concrete FAQ · NRMCA — Concrete in Practice (CIP) Technical Information Series · NRMCA — CIP 31: Ordering Ready Mixed Concrete
Frequently Asked Questions
How much does a cubic yard of concrete cover?
At 4 inches thick, one cubic yard covers 81 square feet. At 6 inches thick, it covers 54 square feet. At 3 inches thick, it covers 108 square feet.
How many bags of concrete are in a cubic yard?
Approximately 45 bags of 80 lb concrete or 60 bags of 60 lb concrete make one cubic yard. For large projects, ordering ready-mix by the yard is more economical.
How thick should a concrete slab be?
4 inches is standard for patios and walkways. Driveways should be 5-6 inches. Garage floors typically need 4-6 inches. Heavy traffic areas may need reinforcement.
Should I add extra concrete?
Yes, add 5-10% extra for waste, spillage, and uneven subgrade. For complex shapes or sloped ground, add 15%. Its better to have a little extra than to run short.
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