Paint Calculator
Gallons of paint needed for a room, minus doors and windows.
Check the can. 350 is typical; use 250 to 300 for bare or textured walls.
You need
1.7 gallons
Buy 2 gallon(s) to be safe, or round the remainder to quarts.
- Paintable wall area
- 301 sq ft
- Total area to cover (2 coats)
- 602 sq ft
Estimates only. Verify quantities before ordering.
How this is calculated
Wall area = 2 x (length + width) x ceiling height, minus 21 sq ft per door and 15 sq ft per window. Gallons = wall area x coats / coverage per gallon. The purchase figure rounds up to whole gallons.
This calculator estimates wall paint for a rectangular room. It computes the total wall area from the room dimensions and ceiling height, subtracts a standard allowance for each door (21 sq ft) and window (15 sq ft), multiplies by the number of coats, and divides by the coverage rate printed on the can.
Most interior latex paints cover 350 to 400 square feet per gallon on a smooth, previously painted surface. Drop the coverage number to 250 to 300 if you are painting bare drywall, heavily textured walls, or making a drastic color change, because the first coat will soak in more.
Paint for common room sizes
Rows assume 8 ft ceilings, one door, two windows, two coats, and 350 sq ft per gallon. Round up to whole gallons when you buy.
| Room size | Gallons | Wall area |
|---|---|---|
| 10 x 10 ft (small bedroom) | 1.5 gallons | 269 sq ft |
| 12 x 10 ft (bedroom) | 1.7 gallons | 301 sq ft |
| 12 x 12 ft | 1.9 gallons | 333 sq ft |
| 15 x 12 ft (living room) | 2.2 gallons | 381 sq ft |
| 20 x 15 ft (great room) | 2.9 gallons | 509 sq ft |
Choosing a sheen
Sheen is a durability decision more than an aesthetic one. Flat hides surface imperfections best and scrubs worst, which suits ceilings and low-traffic adult bedrooms. Eggshell and satin add washability with modest sheen and cover most walls in a house. Semi-gloss and gloss are the most scrubbable and the most reflective, which is why they go on trim, doors, kitchens, and bathrooms.
The trade-off runs in both directions: higher sheen resists moisture and cleaning but highlights every roller mark, patch, and drywall imperfection, particularly on a long wall in raking light. On a wall with a history of repairs, dropping a step in sheen hides more than another coat will.
Modern paints have narrowed this gap considerably, and premium flat and matte products now offer washability that used to require eggshell. If you want a flat look in a hallway, it is worth paying for a scrubbable matte rather than accepting a sheen you dislike.
When primer is actually needed
Primer is not required for every repaint. Painting a similar color over a sound, previously painted wall in the same sheen usually needs no primer at all, and self-priming paints handle that case well. Primer earns its place in specific situations rather than as a default extra coat.
Use it on bare drywall, where the paper and the joint compound absorb very differently and will otherwise flash through the topcoat. Use it over bare wood, over stains, water marks, smoke, or crayon that would bleed through, and over glossy surfaces where you need adhesion. Use a tinted primer when covering a dramatic color change, since it does more to hide the old color than an extra finish coat and costs less.
Skipping primer where it is needed usually shows up as an uneven sheen rather than poor coverage. The wall looks patchy in certain light even though the color is uniform, and the fix at that point is priming and repainting the whole surface.
What changes real-world coverage
The 350 to 400 square feet per gallon on the can assumes a smooth, previously painted, non-absorbent surface. Texture is the biggest variable: a knockdown or orange peel wall can drop coverage by 10 to 20 percent, and heavy texture or popcorn ceiling substantially more, because the actual surface area is larger than its footprint.
Color and application method matter too. Deep reds, bright yellows, and some organic pigments have poor hiding and may need three coats regardless of quality, which is why deep bases often carry a coverage warning. Spraying wastes more material than rolling through overspray and priming the lines, though it lays down a better finish on trim and doors.
Buy a little more than the calculation, and buy it in one batch. Paint is tinted per order and two gallons mixed weeks apart can differ slightly, which is visible on a large wall. Keeping a labeled quart for touch-ups is worth more than returning it, since matching a faded wall years later is much harder than opening the original can. For gallons by room size and how ceilings and trim are counted separately, see our guide on how many gallons of paint you need.
Common questions
How much does one gallon of paint cover?
About 350 to 400 square feet per coat on smooth, previously painted walls. Porous surfaces like new drywall, plaster patches, or heavy texture absorb more, so plan on 250 to 300 square feet per gallon for the first coat in those cases.
Do I really need two coats?
Almost always, yes. One coat rarely gives uniform color and sheen, even with paint-and-primer products. The exceptions are repainting with the exact same color or using very high-end paint over a similar shade. Budget two coats and treat one-coat results as a bonus.
Do I need primer as well?
Prime when painting bare drywall or wood, covering stains or repairs, switching from a dark color to a light one, or painting over glossy surfaces. If the walls are already painted, in good shape, and the color change is mild, a quality self-priming paint is usually enough.
Does this calculator include the ceiling?
No, it covers walls only, since ceilings are usually painted in a different product and finish. To estimate ceiling paint, multiply room length by width for the area, then divide by your coverage rate and multiply by coats. A 12 x 10 room ceiling is 120 sq ft, roughly a third of a gallon per coat.