Paint Calculator: How Much Paint for Walls, Ceiling & Trim

Use this paint calculator to find how much paint you need for a room. Enter the room size, the number of coats and the coverage from the can. You get the gallons for the walls, ceiling and trim, plus primer if you need it, as a shopping list in gallons and quarts.

Room length

Room width

Wall height

Doors

doors

Windows

windows

Paint the ceiling Paint the trim (baseboards, door and window casing)

Wall area to paint

sq ft

Coats

Coverage per gallon

sq ft

Add one coat of primer (new drywall or a big color change)

Cost

Paint price per gallon

Primer price per gallon

Painter's labor per sq ft painted

–gallons of wall paint

What to buy

–sq ft of walls

–sq ft of ceiling

–ft of trim

–estimated cost

Coverage on the can comes first. Rough or porous surfaces and dark colors need more paint. Quarts are suggested when they cover the rest.

How the paint calculator works

Wall area = 2 × (room length + room width) × wall height, minus 21 sq ft per door and 15 sq ft per window
Gallons = area × coats ÷ coverage per gallon (350 sq ft by default)
Ceiling = room length × width, at the same coats and coverage
Trim = baseboard around the room, plus 17 ft of casing per door and 16 ft per window, counted 4 in wide
Primer = one coat over the walls and ceiling at 300 sq ft per gallon
Shopping list: gallons are rounded up to quarts, and 3 quarts become a gallon because a gallon usually costs about the same

Worked example

A 14 × 12 ft bedroom with 8 ft walls, one door, two windows, 2 coats, paint that covers 350 sq ft per gallon:

Walls: 2 × (14 + 12) × 8 = 416 sq ft, minus 51 sq ft for openings = 365 sq ft
Wall paint: 365 × 2 ÷ 350 = 2.09 gallons, so buy 2 gallons + 1 quart
Ceiling paint: 168 × 2 ÷ 350 = 0.96 gallons, so 1 gallon
Trim: 52 ft of baseboard + 17 + 2 × 16 ft of casing = 101 ft. 101 × 4 ÷ 12 = 33.7 sq ft, × 2 ÷ 350 = 0.19 gallons, so 1 quart
Primer, if needed: (365 + 168) ÷ 300 = 1.78 gallons, so 2 gallons

Paint for common rooms

For 8 ft walls, one door, two windows, 2 coats at 350 sq ft per gallon:

Room	Wall area	Wall paint	Ceiling paint
10 × 10 ft	269 sq ft	1.54 gal	0.57 gal
10 × 12 ft	301 sq ft	1.72 gal	0.69 gal
12 × 12 ft	333 sq ft	1.90 gal	0.82 gal
14 × 12 ft	365 sq ft	2.09 gal	0.96 gal
16 × 14 ft	429 sq ft	2.45 gal	1.28 gal
20 × 16 ft	525 sq ft	3.00 gal	1.83 gal

Coverage by surface

These are typical ranges. The coverage printed on your can comes first.

Surface	Typical coverage per gallon
Smooth, painted drywall	350 to 400 sq ft
New drywall over primer	300 to 350 sq ft
Textured walls or ceilings	250 to 300 sq ft
Bare wood trim	300 to 350 sq ft

Tips for painting a room

Prime new drywall, patches and stained areas. Primer also helps when you go from a dark color to a light one.
Plan two coats for an even finish. One coat is often enough only when you repaint the same color.
Paint the ceiling first, then the walls, then the trim.
Mix all gallons of the same color in one bucket before you start (called boxing), so the color stays even.
Keep the leftover quart, labeled with the room, for touch-ups later.
For a new wall, the drywall calculator covers the board and mud. For an outdoor job, the deck and fence stain calculator works out stain.

Frequently asked questions

How much paint do I need for a room?

Multiply the wall area by the number of coats, then divide by the coverage on the can. A 12 × 12 ft room with 8 ft walls, one door and two windows has about 333 sq ft of wall, so 2 coats at 350 sq ft per gallon take about 1.9 gallons. Most people buy 2 gallons.

How many square feet does a gallon of paint cover?

Most interior paint covers about 350 to 400 sq ft per gallon on smooth walls. Textured, porous or bare surfaces take more paint, so a gallon may cover only 250 to 300 sq ft.

How much paint do I need for trim?

Much less than for walls. Baseboards and casing in a normal bedroom are around 100 ft of trim, which is under a quarter gallon for 2 coats. A quart is usually enough for one room.

Do I need primer before painting?

Use primer on new drywall, patched areas, stains, bare wood and big color changes. On clean walls that were painted before, a good paint can often go straight on. Primer covers about 300 sq ft per gallon.

How much does it cost to paint a room?

It depends on the paint you choose and labor where you live, and prices vary a lot by region. Enter your price per gallon and a painter’s price per square foot from a local quote to get a total.

Results are estimates for planning. Coverage depends on the paint, the color and the surface, so check the can. See How We Calculate for the formulas we use.