MicroCalculatorsConcrete Calculator
Estimate cubic yards of concrete for slabs, footings, or rectangular forms. Volume = length × width × depth, then ÷ 27 for cubic yards.
Length in feet.
Width in feet.
4 in typical for slabs. Enter depth in inches.
Result:
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Concrete Calculator — FAQ
- How many bags of concrete do I need per yard?
- One cubic yard ≈ 45 80-lb bags or 60 60-lb bags. Check bag coverage.
- What thickness is recommended for patios?
- 4 inches is typical for patios. Driveways often 4–6 inches.
- How do I calculate concrete for post holes?
- Volume = π × radius² × depth. Use radius in feet, depth in feet, divide by 27 for cubic yards.
How Much Concrete Do I Need?
Concrete volume for a rectangular slab is length × width × depth, all in the same units. In feet, that gives cubic feet; divide by 27 to get cubic yards. One cubic yard covers 81 square feet at 4 inches thick, or 54 sq ft at 6 inches.
Order 5–10% extra for spillage and uneven subgrade. Ready-mix is sold by the yard; bags are typically 40–80 lb. One cubic yard ≈ 45 80-lb bags. For post holes, use π × radius² × depth, then divide by 27.
People Also Ask
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Want to learn more?
Read our full guide: How Much Concrete Do I Need? — volume formulas for slabs, footings, and post holes, plus bags vs ready-mix.
Last updated: February 2026