How Much Paint Do I Need? A Room-by-Room and Whole-House Guide
Most rooms need about two gallons of wall paint for two coats, and most two-story exteriors need 10 to 20 gallons of siding paint plus a few gallons for trim. The exact number comes from three things: the square feet of surface, the coverage printed on the can, and the number of coats.
This guide shows how to measure, which surfaces to count separately, and where people usually run short.
Step 1: Measure the Wall Area
For each wall, multiply the length by the height. Add the walls together. A 12 by 14 foot room with 8-foot ceilings has a perimeter of 52 feet, so the walls are 52 × 8 = 416 square feet.
Subtract large openings only. A standard door is about 20 square feet and a typical window about 15. Small windows and outlets are not worth subtracting; the extra paint covers waste and touch-ups.
Step 2: Check the Coverage on the Label
Most interior and exterior acrylic paints list coverage of roughly 350 to 400 square feet per gallon on smooth, primed surfaces. Rough or porous surfaces drink more: textured drywall, bare wood, stucco, rough siding and masonry can cut coverage by a quarter or more. Use the low end of the label range unless the surface is smooth and already painted.
Step 3: Multiply by the Number of Coats
Two finish coats is the standard for even color and full film thickness. So the 416 square foot room above, minus one door and two windows (about 50 square feet), is 366 square feet per coat, or 732 square feet for two coats. At 350 square feet per gallon, that is just over two gallons.
| Room size (8 ft ceilings) | Wall area (one coat) | Gallons for two coats |
|---|---|---|
| 10 × 10 bedroom | about 300 sq ft | 2 |
| 12 × 14 bedroom | about 365 sq ft | 2 to 2.5 |
| 14 × 18 living room | about 450 sq ft | 2.5 to 3 |
| 20 × 20 great room, 10 ft walls | about 700 sq ft | 4 |
Ceilings, Trim and Doors
Ceilings are measured as length × width. A 12 by 14 ceiling is 168 square feet, so one gallon of ceiling paint usually covers two coats.
Trim is usually bought by the quart. A typical bedroom's baseboards, door casing and window casing need about a quart for two coats; a whole house of trim and doors often takes one to two gallons of semi-gloss.
Exteriors
Measure each side of the house: length × height to the eaves, plus the triangle of each gable (half the base × the height). A two-story house of 2,000 square feet of floor area often has 2,500 to 3,500 square feet of paintable siding. At 350 square feet per gallon and two coats, that is 15 to 20 gallons for the body. Trim, fascia, soffits and doors are figured separately, often 3 to 6 gallons.
Rough or weathered siding, and bare wood after scraping, use more. So does going from a dark color to a light one.
Where People Run Short
- Color changes. A big change from dark to light can need a primer coat or a third coat.
- New drywall and patches. Unprimed drywall and joint compound soak up paint; prime first.
- Textured walls and ceilings. Knockdown and orange peel textures have more surface than flat walls.
- Spraying. Airless sprayers use more paint than rolling because some is lost as overspray, often a quarter more or so, depending on the setup.
Buy It All at Once
Custom-tinted paint can vary slightly between batches. For a large job, buy the whole amount at once, or mix gallons together in a five-gallon bucket ("boxing") so the color is consistent from wall to wall. Keep one labeled quart of every color for touch-ups.
Frequently Asked Questions
How much paint does a 12 by 12 room need?
About two gallons for two coats on the walls, plus one gallon of ceiling paint and a quart of trim paint.
Is one gallon enough for a bedroom?
For one coat in a small bedroom, sometimes. For two coats, plan on two gallons.
Does primer reduce how much paint I need?
On new drywall, patches and stained or porous surfaces, yes. Primer seals the surface so the finish coats cover evenly instead of soaking in.
How much paint does it take to paint a house exterior?
For a typical two-story house, about 15 to 20 gallons for siding and 3 to 6 gallons for trim, at two coats. Measure each side to be sure.
Let Us Do the Math
When we give an estimate, the product list and gallon count are part of the written scope, so there is no running back to the store mid-job. See our interior painting service or contact us to book a walkthrough.