Paint Calculator
Work out how many gallons of paint a room or wall needs.
What you'll need to order
- interior wall paint
- ceiling paint
- primer
- painter's tape
- rollers and brushes
Prices vary by region and haul distance. Get quotes from at least two local suppliers.
How this calculator works
gallons = wall area ÷ 350 × number of coats
A gallon covers roughly 350 sq ft per coat on smooth, previously painted drywall. Textured, porous or new surfaces drop that to 250 or 300, and dark-over-light colour changes need primer regardless of coat count.
Switch the site to metric — the control is in the footer — and your inputs, your results and the tables below follow. The formula, the constants, the guidance text and the sources stay in US units on purpose: that is how the standards they come from are written, and restating them would detach each figure from the document you are meant to be able to check it against.
Where these numbers come from
- ASTM D344 (Relative Hiding Power of Paints) 2023 — the spreading-rate method; 350 sq ft per gallon is a typical manufacturer figure for smooth primed drywall
Check the edition. Codes are amended every few years, and the one your inspector works from may not be the one named above.
Worked example
With room length 14 ft, room width 12 ft, ceiling height 8 ft, number of coats 2 , this calculator returns 2.15 gal.
Paint needed by room size
Figures below assume room width 12 ft × ceiling height 8 ft × number of coats 2 . Each row is a link that fills in the calculator above. Send one and the other end sees the same figures you do.
| Room length | Wall paint needed (gal) | Wall area (sq ft) |
|---|---|---|
| 8 ft | 1.60 | 280.0 |
| 10 ft | 1.78 | 312.0 |
| 12 ft | 1.97 | 344.0 |
| 14 ft | 2.15 | 376.0 |
| 16 ft | 2.33 | 408.0 |
| 20 ft | 2.70 | 472.0 |
Rooms 12 ft wide with 8 ft ceilings, two coats, with 40 sq ft deducted for a door and a window.
How much paint for a bedroom, bathroom or whole house?
Every row here opens the calculator already filled in. Copy that link and the numbers travel with it.
| Job | Size | Wall paint needed | Material cost |
|---|---|---|---|
| Small bathroom | 8 ft × 6 ft × 8 ft × 2 | 1.05 gal | $26 – $79 |
| Bedroom | 12 ft × 11 ft × 8 ft × 2 | 1.87 gal | $47 – $141 |
| Living room | 18 ft × 14 ft × 9 ft × 2 | 3.06 gal | $77 – $230 |
| Open-plan kitchen and diner | 24 ft × 16 ft × 9 ft × 2 | 3.89 gal | $97 – $291 |
| Stairwell with high ceiling | 10 ft × 8 ft × 16 ft × 2 | 3.06 gal | $77 – $230 |
Figures are for walls only. Ceilings are shown separately in the calculator — a ceiling takes roughly a third of what the walls do.
Cost range uses $25–$75 per gallon for material only.
What does interior paint cost?
Material typically runs $25 to $75 per gallon. Paint only. A professional interior repaint typically runs $2 to $6 per square foot of floor area, including prep and two coats.
What moves the price:
- Quality tier — contractor-grade versus premium differs mainly in coverage and washability
- Sheen: flat is cheapest, high-gloss and enamel cost more
- Deep or saturated colours need a tinted primer and often a third coat
- Primer, which most jobs over bare or patched drywall need as a separate product
Prices are US averages and move with fuel, season and haul distance. Always get two local quotes before budgeting.
Paint coverage by surface
| Type | Coverage (sq ft per gallon) | Notes |
|---|---|---|
| Smooth primed drywall | 400.0 | Best case; the figure on the tin |
| Previously painted wall | 350.0 | What this calculator assumes |
| Light texture (orange peel) | 300.0 | Texture adds surface area |
| Heavy texture (knockdown) | 250.0 | Spraying is far more efficient here |
| Bare drywall, no primer | 200.0 | Prime instead — it costs less than the extra paint |
| Rough masonry or block | 175.0 | Block filler first on porous surfaces |
Tin coverage figures assume ideal conditions. The 350 sq ft used here is the realistic working figure for a repaint.
Paint quantity questions
How much does a gallon of paint cover?
About 350 sq ft in one coat on smooth, previously painted drywall. New drywall, textured walls and masonry soak up far more — expect 250 sq ft or less.
How many gallons do I need for a 12x14 room?
Just over two gallons for two coats on the walls, plus one gallon for the ceiling. Buy the extra quart rather than running out — matching a second batch of tinted paint is never exact.
Do I need primer?
Yes on bare drywall, over stains, and whenever you are covering a dark colour with a lighter one. Over an existing paint film in a similar shade, two coats of a quality paint will do without it.
How much paint do I need for a 12x12 room?
About 1.5 gallons for two coats on the walls, assuming an 8 ft ceiling. Add roughly half a gallon if you are painting the ceiling as well.
How much paint for a whole house interior?
A 2,000 sq ft home typically takes 12 to 16 gallons for walls and 4 to 6 for ceilings, at two coats. Trim and doors need another 2 to 3 gallons of enamel.
How much paint do I need for trim and doors?
A gallon of enamel covers about 6 average doors, or roughly 350 linear feet of baseboard. Most whole-house repaints need 2 to 3 gallons of trim paint.
Should I subtract windows and doors?
This calculator already deducts 40 square feet, about one door and one average window. If your room has a wall of glass or several large windows, subtract the extra area yourself.
Is one coat of paint ever enough?
Only when repainting the same colour on a sound surface, or with a paint-and-primer product over a very close shade. Every other case shows lap marks and uneven sheen after a single coat.