Concrete calculator
Concrete slab calculator
Use this concrete slab calculator to figure concrete for a slab, patio, driveway, floor, or pad. Enter the dimensions to estimate cubic yards or cubic metres, choose an extra allowance, and review the volume calculation.
Slab / pad estimate
Measurement system: Imperial. Planning estimate based on the dimensions and allowance shown below.
Build your estimate
Choose a shape, enter measured dimensions, then review every step.
Enter the dimensions of the concrete itself. This estimate does not subtract posts or wall openings.
Bag yields and product settings
Yield differs by product. These common examples are editable.
Bag counts are rounded up. The 40, 50, 60, and 80 lb rows show common US products; use the package yield for your product.
Optional: price your materials
Enter local prices. No regional or supplier price is assumed.
Material estimate only. Delivery, taxes, labor, and supplier minimums are not included.
Formula and assumptions
How to calculate slab concrete
Convert slab thickness to the same unit as its length and width, multiply the dimensions, then convert the volume. If your dimensions are in feet and inches:
Worked example: a 10 ft × 10 ft slab, 4 in thick
- Convert 4 inches to feet: 4 ÷ 12 = 0.3333 ft.
- Calculate the net volume: 10 × 10 × 0.3333 = 33.33 ft³.
- Convert to cubic yards: 33.3333 ÷ 27 = 1.2346 yd³.
- If you choose 10% extra, 1.2346 × 1.10 = 1.3580 yd³, displayed as 1.36 yd³.
Allowance and bag yield
For a 100 ft² footprint, changing the specified thickness from 4 to 6 inches increases the net volume from 1.235 to 1.852 yd³. Use the project’s specified thickness; these values illustrate quantity changes and do not recommend a structural design.
The allowance is your planning choice. Uneven ground, excavation, forms, handling, and the supplier’s order increments can affect what you need. Bag equivalents use the mixed concrete yield you enter and round up to whole bags. Common bag examples are not a substitute for the yield printed on your specific product.
For a slab with several sections, calculate each section and add the volumes. This calculator currently estimates one rectangular pour at a time.
Concrete pad quantities and supplier costs
A patio, driveway section, floor, or equipment pad can share the rectangular volume formula while having different project specifications. Work out the concrete amount first, then price that quantity with the local supplier’s unit and billing rules.
Compare cubic yards and bag quantities for a 12 × 16 ft concrete pad, or use the concrete price per yard guide to separate material, delivery and billed quantity.