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Gallons by wall length
| Wall length × 8 ft | 1 coat | 2 coats |
|---|---|---|
| 60 ft | 1.4 gal | 2.7 gal |
| 90 ft | 2.1 gal | 4.1 gal |
| 120 ft | 2.7 gal | 5.5 gal |
| 150 ft | 3.4 gal | 6.9 gal |
| 180 ft | 4.1 gal | 8.2 gal |
At 350 sq ft per gallon, no openings deducted.
Sherwin-Williams says a gallon typically covers 350–400 square feet. New drywall soaks up more, so prime it first. Bare concrete block takes much more paint per coat than drywall.
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
The example has 888 sq ft of wall after openings. Two coats at 350 sq ft per gallon need 5.1 gallons, so buy 6. Painting the 712 sq ft ceiling in one coat adds 2.0 gallons. If you prime new drywall first, budget a separate primer coat over the same area.
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.
Common questions
How much paint for a basement?
Wall area × coats ÷ 350. For 120 ft of 8 ft wall with two coats, about 5.5 gallons.
Do I need primer on new drywall?
Yes. New drywall and joint compound absorb paint unevenly; a primer coat evens it out and saves finish paint.
Related calculators
Sources
- https://www.sherwin-williams.com/en-us/color/color-tools/paint-calculator
- 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