Paint Calculator
Estimate how many gallons of paint you need for a room or wall based on the total wall length, height, and number of coats.
How this is calculated
Wall area is calculated as total wall length × height. This calculator does not automatically subtract doors and windows, so for more precision subtract roughly 20 ft² per standard door and 15 ft² per standard window from your wall length × height total. That area is multiplied by the number of coats, then divided by standard paint coverage of 350 ft² per gallon (actual coverage varies by paint brand, sheen, and surface texture). We add your selected waste percentage for cutting-in, touch-ups, and uneven surfaces, then round up to the nearest quart.
The material weights, waste allowances, and rounding rules behind every calculator are documented on our methodology page.
Example calculation
How much paint common room sizes need
These figures assume 8 ft walls, 350 ft² of coverage per gallon, and a 10% waste allowance, with no deduction for doors or windows. One coat suits a refresh in a similar color, and two coats is the standard for a new color or fresh drywall.
| Room size | Wall length | Wall area | 1 coat | 2 coats |
|---|---|---|---|---|
| 10 × 10 ft | 40 ft | 320 ft² | 1.0 gal | 2.0 gal |
| 12 × 12 ft | 48 ft | 384 ft² | 1.2 gal | 2.4 gal |
| 12 × 14 ft | 52 ft | 416 ft² | 1.3 gal | 2.6 gal |
| 14 × 16 ft | 60 ft | 480 ft² | 1.5 gal | 3.0 gal |
| 16 × 20 ft | 72 ft | 576 ft² | 1.8 gal | 3.6 gal |
Paint is sold in quarts, gallons, and 5-gallon pails, so round up. Ceilings, trim, and doors are estimated separately.
Measuring walls and subtracting openings
Add up the length of every wall you will paint and multiply by the ceiling height. For openings, a standard interior door is about 20 ft² and an average window is about 15 ft². Subtract them from the total only if they are large, since small openings are covered by the waste allowance.
Here is a worked example. A 12 × 14 ft room with 8 ft walls has 416 ft² of wall area. With one door and two windows, you subtract 50 ft² and paint 366 ft². For two coats with 10% waste, the calculator needs 2.30 gallons instead of 2.61 gallons without the deduction. Rounded up to the nearest quart, that is 2.50 gallons versus 2.75 gallons, so subtracting openings saves about a quart in this room.
Don't subtract openings when you have a lot of trim, built-ins, or rough surfaces. Large windows still need painted frames, and recesses add surface that flat measurements ignore.
Coverage varies by surface
The 350 ft² per gallon used here is a typical figure for one coat on a smooth, previously painted wall. Porous or rough surfaces absorb more paint, so your real coverage can be much lower.
| Surface | Typical coverage per gallon | Why it changes |
|---|---|---|
| Smooth, previously painted drywall | 350–400 ft² | Sealed surface; best case |
| New drywall with primer | 300–350 ft² | Primer evens out absorption |
| New, unprimed drywall | 200–300 ft² | Paper and joint compound soak up the first coat |
| Textured walls or ceilings | 200–300 ft² | More surface area and deeper valleys |
| Rough stucco, brick, or masonry | 100–200 ft² | Very porous; may need a block filler |
Check the coverage printed on the can, which differs by brand, sheen, and color.
When you need primer
Primer seals porous surfaces, blocks stains, and helps the finish coat grip. It is worth the extra step on bare drywall and patched areas, on glossy surfaces after light sanding, over water or smoke stains, and when you are covering a dark color with a light one.
Tinting the primer toward your final color often saves a coat when you are making a big color change. Be wary of paint-and-primer-in-one products over stains or strong colors. They are usually just thicker paint, so you may still need a dedicated primer and two topcoats. Buy primer separately and estimate it with the same wall area, using the coverage listed on its label.
Choosing a sheen
| Sheen | Best for | Trade-off |
|---|---|---|
| Flat or matte | Ceilings, low-traffic rooms | Hides flaws but is harder to wipe clean |
| Eggshell | Living rooms, bedrooms | Gentle glow with moderate washability |
| Satin | Hallways, kids' rooms, family areas | Easy to clean, shows more roller marks |
| Semi-gloss | Trim, doors, kitchens, baths | Durable and moisture-resistant, highlights imperfections |
| Gloss | Accent doors, cabinets, furniture | Very durable and reflective; needs careful prep |
Ceilings, trim, and doors
Estimate the ceiling by multiplying room length by width, and use a dedicated ceiling paint that spatters less. A 12 × 14 ft ceiling is 168 ft², so one coat takes roughly half a gallon, and two coats take about a gallon.
Trim and doors are usually painted in semi-gloss and are bought by the quart. A standard door is about 20 ft² per side, so both sides with two coats uses around 80 ft², close to one quart. Baseboards, window casings, and crown molding in an average room usually take about a quart for two coats.
Buying and using the paint well
- Buy all the paint for one room at the same time, and mix multiple gallons together (called boxing) so slight batch differences don't show on the wall.
- Keep a labeled quart of leftover paint for touch-ups, with the color name, sheen, and room written on the lid.
- Prep is the biggest factor in a good result: fill holes, sand glossy spots, clean grease or dust, and tape off trim before you open the can.
- Paint with the room ventilated and above the temperature printed on the can, since many latex paints won't cure properly below roughly 50°F.
- Cut in the edges first, then roll the wall while the edge is still wet to avoid visible lap marks.
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Frequently asked questions
Most paints cover 300–400 ft² per gallon for one coat on a smooth, primed surface. Textured walls, unprimed drywall, or darker color changes may reduce coverage significantly.