Paint Calculator

This paint calculator tells you how much paint you need for a room before you head to the store. Enter the room's length, width and wall height, or type in a total wall area, and it subtracts doors and windows, multiplies by the number of coats and divides by your paint's coverage to give gallons.

Results show as a practical buy list, such as 2 gallons plus 1 quart, so you do not overbuy full gallons for a small remainder. You can add the ceiling as a separate figure, change the coverage to match your paint can, and switch to meters and liters if you work in metric.

How to Use the Paint Calculator

1
Enter the room or wall area
Pick Room dimensions and type the length, width and wall height, or pick Total wall area and enter the square footage of all the walls you are painting.
2
Subtract doors and windows
Set how many doors and windows the walls have. The defaults are 20 sq ft per door and 15 sq ft per window; change them if your openings are larger or smaller.
3
Set coats and coverage
Choose 1, 2 or 3 coats and enter the coverage per gallon from your paint label. The default is 350 sq ft per gallon per coat.
4
Add the ceiling if needed
Turn on Include the ceiling. With room dimensions the ceiling is length times width; with total wall area you enter the ceiling area yourself.
5
Read the buy list
The results update as you type: total paint as gallons plus quarts, the exact gallons, net wall area and a separate ceiling figure.

How the paint calculator works

For a rectangular room, the wall area is the perimeter times the wall height. Doors and windows are then subtracted, since you do not paint them. The net area is multiplied by the number of coats, because each coat covers the full surface again, and divided by the coverage rate.

Coverage is the area one gallon covers in a single coat. Most interior wall paints list 350 to 400 sq ft per gallon on the label, so the calculator uses 350 as a slightly conservative default. The exact gallons are then rounded up to whole gallons plus quarts (a quart is a quarter gallon). In metric mode, the default is 8.6 square meters per liter, which is the same 350 sq ft per gallon.

Wall area = 2 × (length + width) × height
Net area = wall area − (doors × door area) − (windows × window area)
Gallons = (net area + ceiling area) × coats ÷ coverage per gallon

Worked example: a 12 x 14 ft bedroom with the ceiling

Take a 12 x 14 ft room with 8 ft walls, one door, two windows, two coats and paint that covers 350 sq ft per gallon.

Wall area: 2 × (12 + 14) × 8 = 416 sq ft.
Openings: 1 door × 20 + 2 windows × 15 = 50 sq ft, so the net wall area is 366 sq ft.
Wall paint: 366 × 2 ÷ 350 = 2.09 gallons, which you buy as 2 gallons plus 1 quart.
Ceiling: 12 × 14 = 168 sq ft, and 168 × 2 ÷ 350 = 0.96 gallons, so 1 gallon of ceiling paint.
Total: 3.05 gallons. Because walls and ceilings usually take different paint, buy them as separate products.

Paint needed for common room sizes

Figures assume 8 ft walls, one door (20 sq ft), one window (15 sq ft), two coats and 350 sq ft per gallon, rounded up to gallons plus quarts the same way the calculator does.

Room	Net wall area	Wall paint	Buy for walls	Ceiling paint (2 coats)
10 × 10 ft	285 sq ft	1.63 gal	1 gal + 3 qt	0.57 gal
10 × 12 ft	317 sq ft	1.81 gal	2 gal	0.69 gal
12 × 12 ft	349 sq ft	1.99 gal	2 gal	0.82 gal
12 × 14 ft	381 sq ft	2.18 gal	2 gal + 1 qt	0.96 gal
14 × 16 ft	445 sq ft	2.54 gal	2 gal + 3 qt	1.28 gal
16 × 20 ft	541 sq ft	3.09 gal	3 gal + 1 qt	1.83 gal
20 × 20 ft	605 sq ft	3.46 gal	3 gal + 2 qt	2.29 gal

Tips and common mistakes

Use the coverage figure on your actual can. Premium and one-coat paints may list more; textured, porous or unpainted surfaces soak up more, so use a lower number such as 250 to 300.
Plan on two coats for most walls. One coat can work when you repaint the same color over a sound surface; a big color change, especially light over dark, may need a third coat or a tinted primer.
Primer is not included. New drywall, bare wood and patched areas usually need a coat of primer first, which you can estimate by running the calculator again with one coat and the primer's coverage.
Trim, doors and cabinets are not part of the wall estimate and are usually a different sheen. A quart often covers the trim in an average room.
Keep a little leftover for touch-ups, and note the color formula. If you need several gallons, mixing them together in a bucket (boxing) keeps the color consistent from wall to wall.

Quarts, gallons and small jobs

When the total is under a gallon, such as an accent wall or a small bathroom, the calculator shows how many quarts you need. Once you need three quarts, a single gallon may cost about the same, so compare prices before you decide. For large jobs, 5 gallon buckets are another option; divide the gallons figure by 5 and round down, then top up with single gallons.

Features

Room dimensions or total wall area input
Subtracts doors and windows with editable sizes
Adjustable coats and coverage per gallon (default 350 sq ft)
Optional ceiling, shown separately
Buy list in gallons plus quarts for small jobs
US units or metric (meters, liters)

Frequently Asked Questions

How much paint do I need for a 12x12 room?

A 12 x 12 ft room with 8 ft walls has 384 sq ft of wall. Subtract one door (20 sq ft) and one window (15 sq ft) to get 349 sq ft. At two coats and 350 sq ft per gallon, that is 1.99 gallons, so buy 2 gallons for the walls. The ceiling is 144 sq ft, which needs 0.82 gallons for two coats, so add 1 gallon of ceiling paint.

How many square feet does a gallon of paint cover?

Most interior wall paints list 350 to 400 sq ft per gallon for one coat on a smooth, primed surface. With two coats, one gallon covers about 175 to 200 sq ft of wall. Rough, textured or porous surfaces such as new drywall, stucco or bare wood absorb more, so coverage can drop well below the label figure. Check your can and enter its number in the calculator.

How much paint do I need for 1,000 square feet?

For 1,000 sq ft of wall at two coats, you are painting 2,000 sq ft in total. At 350 sq ft per gallon that is 5.71 gallons, which the calculator rounds to 5 gallons plus 3 quarts; at that point a sixth gallon is usually the simpler buy. If your paint covers 400 sq ft per gallon, you need exactly 5 gallons.

Should I subtract doors and windows when calculating paint?

Yes, for an accurate figure. A standard interior door is about 20 sq ft and a typical window about 15 sq ft, which are the calculator's defaults. One door and two windows remove 50 sq ft, or about 0.29 gallons over two coats. In a room with few openings the difference is small, so if you are unsure, leaving them in simply gives you a little extra paint.

Do I really need two coats of paint?

Usually, yes. Two coats give even color and sheen and hide roller marks, and most paint coverage figures assume you will apply two. One coat can be enough when you repaint the same or a very similar color over a clean, sound surface. Going from dark to light, or painting fresh drywall, may need a primer coat plus two coats of finish paint.

How much paint do I need for an accent wall?

A 12 ft wide, 8 ft tall accent wall is 96 sq ft. At two coats and 350 sq ft per gallon, you need about 0.55 gallons, which rounds up to 3 quarts. Because three quarts often cost about as much as a single gallon, many people buy the gallon and keep the rest for touch-ups. Deep, saturated colors may need a third coat.

Last reviewed September 21, 2026