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Yards by area
| Area | 3½ in | 4 in | 5 in |
|---|---|---|---|
| 200 sq ft | 2.16 | 2.47 | 3.09 |
| 500 sq ft | 5.40 | 6.17 | 7.72 |
| 800 sq ft | 8.64 | 9.88 | 12.35 |
| 1000 sq ft | 10.80 | 12.35 | 15.43 |
| 1500 sq ft | 16.20 | 18.52 | 23.15 |
| 2000 sq ft | 21.60 | 24.69 | 30.86 |
Cubic yards, no waste.
Cubic yards = area (sq ft) × thickness (in) ÷ 12 ÷ 27
Patching a trench for new drains takes much less, but the formula is the same.
Measuring the example basement
The worked examples on these pages use the same basement so you can follow one project through every material: 32 × 26 ft (832 sq ft of floor), 116 ft of perimeter wall, and 7′ 8″ from the slab to the underside of the joists. About 120 sq ft around the furnace and water heater stays unfinished, and the finished room has one door (about 20 sq ft) and two small windows (about 10 sq ft each).
Worked example
A new drain trench 30 ft long and 18 in wide, patched 4 in thick, is 45 sq ft × 4 in ÷ 12 = 15 cu ft, or 0.56 cubic yards before waste. Pouring a full new 4 in slab over the example's 832 sq ft would take 10.27 cubic yards, or 10.79 with 5% waste.
Mistakes that change the count
- Measuring the outside of the foundation. Interior walls stand 2–4 in in from the concrete once foam and studs go in, which shortens every wall slightly. The difference is small; round up rather than trim the order.
- Forgetting soffits. Boxes around ducts and beams add wall and ceiling surface that never shows on a floor plan.
- Skipping waste. Basements are full of cut-outs for posts, panels and pipes. 10% waste is a sensible default for sheet goods.
- Buying for the floor, not the walls. Wall area in a basement is often larger than floor area: here the walls are 928 sq ft at 8 ft against 832 sq ft of floor.
Ordering and delivery tips
- Round up to full units: sheets, boxes, gallons and bags are not sold in fractions.
- Check the basement stair turn before buying 12-ft drywall or long trim; it may not fit down the stairs.
- Let flooring acclimate in the basement for the time printed on the carton.
- Keep a few spare boxes or sheets of the same batch for repairs.
- Store drywall and wood off the slab on blocks.
Ready-mix or bags?
Small patches, such as a drain trench, are easier with bagged mix. A full slab is a ready-mix job: order in quarter-yard steps, plan a pump if the truck cannot reach a basement window, and have the crew and tools ready when it arrives.
Common questions
How much concrete for a 1,000 sq ft basement floor?
At 4 in thick, 12.35 cubic yards before waste.
How thick is a basement slab?
Use the thickness your plans or inspector specify; 4 in is the common figure used in the tables here.
Related calculators
Sources
- https://www.homeadvisor.com/cost/basements/
- https://www.blockrenovation.com/guides/basement-remodel-cost-per-square-foot-2026
- https://trusscore.com/blog/the-cost-to-finish-a-basement-in-2024.html