Concrete Calculator
Calculate how much concrete you need for slabs, footings, or columns. Get cubic yards, bag counts, and a rough cost range — bags vs. ready-mix.
- 60 lb bags
- 81
- 80 lb bags
- 61
- Est. cost (bags)
- $366
- Est. cost (ready-mix)
- $229
Cost is rough estimate based on 2026 US averages. Get a local quote before ordering.
The concrete formula
Volume is just length × width × depth (for slabs and footings) or π × r² × height (for columns). The trick is converting to the unit your supplier uses: cubic yards in the US, cubic meters in metric markets.
Bag yields are standard: an 80 lb bag of pre-mix yields about 0.6 cubic feet, a 60 lb bag about 0.45 cubic feet.
Always add a waste factor (10% default). Real pours have spillage, over-excavation, and last-minute fixes. Better to have 5% extra than to run out mid-pour.
Frequently asked questions
Yes — even careful pours have spillage, over-excavation, and form irregularities. 10% is a safe default for slabs; 15-20% for complex shapes or rough ground.
80 lb bags are more efficient cost-per-pound and faster to mix in bulk. 60 lb bags are easier to lift one-handed and good for small repairs. For anything over ~½ cubic yard, consider ready-mix delivery instead.
Usually above 1 cubic yard. Ready-mix runs ~$140-180 per cubic yard delivered (varies by region and minimum-load fees). A cubic yard is 60 bags of 80 lb mix at ~$6 each = $360+ just for material, so delivery wins quickly.
4 inches for sidewalks, patios, and light foot traffic. 5-6 inches for driveways and garages. 8 inches for heavy vehicle traffic or footings. Always check local code.
No — this only calculates concrete volume. Rebar and welded wire mesh add cost but don't change concrete volume. Plan separately.
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