How much paint you need: the gallons and labor math
Every paint can lists a coverage figure — say 350 square feet per gallon — and that number alone is enough to plan a job on paper before you buy anything. The method is one division, one rounding rule, and two multiplications.
The method
Gallons needed = (area × number of coats) ÷ coverage per gallon, rounded up to a whole can — paint stores don't sell fractions of a gallon, and a half-can short means a second trip. Paint cost = gallons × price per gallon. Labor cost = hours × hourly rate. Total = paint cost + labor cost.
A bedroom, two coats
400 square feet of wall, two coats, a paint that covers 400 sq ft per gallon at $38 a gallon, and 6 hours of labor at $35/hr.
- Gallons: (400 × 2) ÷ 400 = 800 ÷ 400 = 2.0 — already a whole number, so 2 gallons.
- Paint cost: 2 × $38 = $76.00.
- Labor: 6 × $35 = $210.00.
- Total: $76.00 + $210.00 = $286.00.
A full exterior, where rounding up matters
2,200 square feet of siding, two coats, a paint that covers 300 sq ft per gallon at $52 a gallon, and 24 hours of labor at $45/hr.
- Gallons: (2,200 × 2) ÷ 300 = 4,400 ÷ 300 ≈ 14.67 — rounds up to 15 gallons, not 14. Buying 14 leaves the job about two-thirds of a gallon short on the last wall.
- Paint cost: 15 × $52 = $780.00.
- Labor: 24 × $45 = $1,080.00.
- Total: $780.00 + $1,080.00 = $1,860.00.
Why you always round up, even for a tiny job
A 150 sq ft accent wall, one coat, coverage 350 sq ft/gal, $42 a gallon, 1.5 hours at $40/hr.
- Gallons: (150 × 1) ÷ 350 ≈ 0.43 — rounds up to 1 gallon, because there's no such thing as buying 0.43 of a can.
- Paint cost: 1 × $42 = $42.00.
- Labor: 1.5 × $40 = $60.00.
- Total: $42.00 + $60.00 = $102.00.
Rounding up on a small job feels wasteful — you'll have leftover paint — but rounding down is the version that actually costs you: a second store trip, a slightly different batch tint, and the extra hours to finish a wall you already started.
The coverage number is the one to double-check
The "350 sq ft/gal" printed on a can assumes a smooth, previously painted surface and one uninterrupted coat. New drywall, stucco, cinder block, or anything unpainted soaks up far more — manufacturers often quote 200–250 sq ft/gal for a porous first coat on bare drywall. Since gallons scale directly with the coverage figure in the denominator, a coverage number that's off by 30% moves your gallon count — and your total — by roughly the same 30%. When in doubt, use the more conservative (lower) coverage figure for the surface you're actually painting, not the number on the label for a best-case wall.
What this doesn't include
This is paint and labor only. Primer, trim, ceilings and any prep work (patching, sanding, taping) are separate line items with their own area and coverage — run the numbers again for each one rather than folding them into a single area figure, since they typically use different products at different coverage rates.
Run your own numbers
The free Paint Job Quote tool runs this instantly for your own area, coats, coverage and rates, entirely on your device.