Paint Calculator

Gallons = wall area less doors and windows × coats ÷ 400 sq ft a gallon: a 12 × 10 ft room with 8 ft walls, a door and two windows has 314 sq ft to paint, or 2 gallons for two coats.

Your measurements

Example

Use the unit shown for each box, or type another one: 12 ft 6 in, 150 in, 3.8 m and 600 mm all work, as do the marks on a tape measure.

Room 1

Length (ft) Width (ft) Wall height (ft) Doors Count them. The door size is in the details below. Windows Other openings you measured (sq ft) An archway, a patio door or any opening not counted above. Extra doors or trim surface (sq ft) Room, color and finish note

Measure from Surfaces Paint coats

Details Package sizes, prices and materials

Extra paint (%) Extra adds paint after the measured surface, coats and coverage are accounted for. Check those inputs first. Primer and trim use their own coverage and coat counts. No percentage here is a manufacturer recommendation. Door width A common door width from a door maker. Change it to your door. Door height 80 inches is the standard door height in rooms with 8-foot ceilings. Window width Window height 32 × 48 inches is one standard window size. Measure yours for a closer answer. Coverage per gallon (sq ft) Can size (gal) Primer coats Primer coverage per gallon (sq ft) Primer can size (gal) Your price per paint can ($) Trim to paint, total length Trim face height Measure the face of the baseboard or casing you will paint. Trim coats Trim paint container (gal)

Example: replace these measurements

Your material list

2 1-gallon paint cans+ 2 more items on the list

314 sq ft measured

Your measured layout

Room dimensions and a schematic door opening. Subtract measured openings. Include the ceiling only when you select it.

Your shopping list

2 1-gallon paint cans
1 1-gallon cans of primer
1 quart of trim paint

Already have some? See what it covers

How many 1-gallon paint cans you have

Quantities and package details

Paintable area: 314 sq ft
Openings deducted: 1 door, 2 windows: 38 sq ft
Area across all coats: 628 sq ft
Paint before can rounding: 1.57 US gal
Paint volume before rounding: 5.94 liters
Surface 1: 314 sq ft
Primer cans: 1
Primer container: 1-gallon can
Baseboard length: 41.5 ft: the room perimeter less the doors
Trim area: 12.1 sq ft
Trim paint: 1 quart of trim paint

The calculation

Surface area: 314 sq ft
ceil(314 × 2 × (1 + 0/100) ÷ 400) = 2

Not measured yet? Common sizes

A rough starting point, worked out with this calculator. 8 ft walls, walls only, one door and two windows, two coats at 400 sq ft per gallon, no extra. Use a row to load its size into the calculator, then change it to your measurements.

Paint for common room sizes
Room	Wall area to paint	Paint before rounding	1-gallon cans
10 × 10 ft	282 sq ft	1.41 US gal	2
12 × 12 ft	346 sq ft	1.73 US gal	2
12 × 14 ft	378 sq ft	1.89 US gal	2
14 × 16 ft	442 sq ft	2.21 US gal	3
16 × 20 ft	538 sq ft	2.69 US gal	3

Common questions

How much paint do I need for a room?

Work out the wall area (the room’s perimeter times its height), subtract the doors and windows, multiply by the coats and divide by the coverage on the can. Sherwin-Williams calls its 400 square feet per gallon a theoretical figure: rough or porous walls take more.

Source: Sherwin-Williams paint questions. Listed on the Sources page.

How many coats of paint do I need?

The paint label and the surface decide. The calculator starts at two coats and counts primer separately, so you can change either.

Do I subtract doors and windows?

Yes. Count them and the calculator multiplies each by a size you can change: 30 by 80 inches for a door and 32 by 48 inches for a window.

Source: Marvin: Best interior door size for your home; Pella: Standard window sizes. Listed on the Sources page.

Should I buy quarts, gallons or a 5-gallon pail?

The size that leaves the least over. Switch the can size in the details to compare. Trim is usually a separate, smaller purchase: enter its length to count it.

How is the ceiling counted?

Choose walls and ceiling to add the room’s floor area as ceiling. Ceiling paint is often a different product, so a separate list may suit you better.

How to plan the quantity

Wall area is the room perimeter times height. Count the doors and windows instead of measuring them: each count is multiplied by the door or window size in the details, which you can change. Add any other opening you measured in square feet. Add the ceiling only when you plan to paint it. Each room keeps its own openings.

Multiply the paintable area by the number of coats. Divide by the coverage on the can and round to the selected can size. Paint and primer have separate coat, coverage and can-size inputs.

A label’s coverage may not match a porous or textured wall. Adjust coverage for the product and surface instead of assuming every gallon does the same job.

Before you order

Enter the trim length in the details to get a separate trim list, usually a different finish in a smaller container. Doors, cabinets and repairs are separate tasks. This does not choose a coating or decide whether primer is needed.
Different colors and finishes need separate purchase lists, even when their areas could be combined.

Have prices moved?

Paint cost 5.9% more in August 2026 than a year earlier (Bureau of Labor Statistics producer price index, preliminary).

Plan the work as well as the order: How to paint a room: prep, coats and cleanup.

Before ordering, read the guide: How much paint do I need? Coverage, coats and primer. Or choose another calculator.