Methodology and sources
Last reviewed 2026-10-22.
Formulas
- Slab: length (ft) x width (ft) x thickness (in) / 12 = cubic feet.
- Footing: length (ft) x width (in) / 12 x depth (in) / 12 = cubic feet.
- Round column: pi x (diameter / 24)^2 x depth (in) / 12 x number = cubic feet. The diameter is in inches, so dividing by 24 gives the radius in feet.
- Cubic yards = cubic feet / 27.
- Extra for waste or settling is a percentage added to the volume. You can change it.
Concrete bags
Bag counts divide the volume with extra by the yield of one bag and round up. Yields are 0.3, 0.375, 0.45 and 0.6 cubic feet for 40, 50, 60 and 80 lb bags, from the Quikrete Concrete Mix data sheet. Other brands and mixes can differ.
Gravel and sand weights
Tons = cubic yards x tons per cubic yard. The default weights are typical values, not measurements. They change with stone size, moisture and the quarry, so ask your supplier and type their number if it is different.
| Material | Tons per cubic yard | Pounds per cubic yard |
|---|---|---|
| Gravel, 1/4 to 2 inch | 1.4 | 2,800 |
| Pea gravel | 1.35 | 2,700 |
| Crushed stone | 1.4 | 2,800 |
| Rock, 2 to 6 inch | 1.25 | 2,500 |
| Sand, dry | 1.35 | 2,700 |
Mulch
Mulch uses the same volume formula. Bags are rounded up to whole bags.
What is not included
Sub-base, rebar, forms, compaction beyond the extra percentage, delivery fees, taxes and local rules. Prices are only what you enter.
Corrections
If you find a mistake, write to us through the contact page.