What is the Concrete Calculator?
A concrete calculator estimates the volume of concrete needed for slabs, footings, columns, steps and curbs in cubic yards, cubic feet and cubic meters — and tells you how many 60 lb or 80 lb bags to buy.
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Concrete Calculator
Estimate concrete volume needed for slabs, footing and columns in cubic yards.
Inputs
Dimensions
Bag Estimate
Results
Bags needed
1
80 lb bag · incl. 5% waste
Volume
0.009 yd³
0.23 cu ft · 0.007 m³
| Metric | Value |
|---|---|
| Cubic feet | 0.23 ft³ |
| Cubic yards | 0.009 yd³ |
| Cubic meters | 0.007 m³ |
| Bags (80 lb bag), exact | 0.39 |
| Bags (incl. 5% waste), rounded up | 1 |
Concrete Calculator formula
Volume = length × width × depth (in feet) = cubic feet. Cubic yards = cubic feet ÷ 27 (because 1 yard³ = 27 ft³). Bags needed = cubic feet ÷ yield per bag (a 60 lb bag yields ~0.45 ft³; an 80 lb bag yields ~0.60 ft³). Always add 5–10% for spillage and uneven subgrade.
How to use the Concrete calculator
- 1Choose your shape: slab, footing, column (round), or column (square).
- 2Enter the dimensions in feet and inches (or meters if using metric).
- 3Enter the depth or thickness of the pour.
- 4Click Calculate to see volume in cubic yards, cubic feet and cubic meters.
- 5Use the bag count to order 60 lb or 80 lb pre-mixed bags from the home center.
Example calculation
A 10 ft × 10 ft patio slab, 4 inches (0.333 ft) thick: volume = 10 × 10 × 0.333 = 33.3 ft³ = 1.23 yd³. With a 10% safety margin, order 1.4 yd³ (about 56 eighty-pound bags, since each yields 0.60 ft³).
Frequently asked questions
- How many bags of concrete do I need?
- Divide the cubic feet of your pour by the yield per bag. An 80 lb bag yields about 0.60 ft³, a 60 lb bag yields about 0.45 ft³. For a 33.3 ft³ slab you need 56 eighty-pound bags (33.3 ÷ 0.60), plus 10% extra for waste.
- How do I calculate cubic yards of concrete?
- Multiply length × width × depth (all in feet) to get cubic feet, then divide by 27 to get cubic yards. Add 5–10% for spillage. Order in quarter-yard increments from a ready-mix supplier.
- How thick should a concrete slab be?
- Patios and walkways: 4 inches. Driveways (residential): 4–6 inches. Footings: at least 8 inches and below the frost line. Heavy loads or commercial slabs: 6+ inches with rebar reinforcement.
- How much does a yard of concrete weigh?
- One cubic yard of cured concrete weighs about 4,050 lb (≈1,835 kg). Wet concrete is similar. A typical 10-cubic-yard ready-mix truck carries about 40,500 lb, so make sure your driveway or subgrade can support the load.
- Should I order by the bag or by the truck?
- Bagged concrete (60 or 80 lb) makes sense for pours under about 1 cubic yard. For anything larger — slabs, driveways, footings — ready-mix delivery is faster, cheaper per yard, and avoids the labor of mixing dozens of bags by hand.
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