How much paint do I need? For a typical room, measure the wall area, subtract doors and windows, divide by about 350 to 400 square feet per gallon, and multiply by two coats. Most average bedrooms take about two gallons for the walls. The steps below show the full calculation so you buy the right amount the first time.
How Much Paint Do I Need: The Basic Formula
Paint is sold by the gallon, and the label states roughly how much area one gallon covers. A common figure is 350 to 400 square feet, but your can will tell you the exact number. Use that number in this formula.
- Measure each wall. Multiply the width by the height in feet.
- Add the walls together. This is your total wall area.
- Subtract openings. Take off roughly 20 square feet for a standard door and about 15 for an average window, or measure them for accuracy.
- Divide by the coverage. Use the number on the can, for example 350.
- Multiply by the coats. Two coats is the usual plan.
- Round up. Buy a little extra for touch-ups.
A Worked Example
Take a room that is 12 feet by 14 feet with 8 foot walls. The perimeter is 12 + 14 + 12 + 14 = 52 feet. Multiply by 8 feet of height and you get 416 square feet of wall. Subtract one door (20) and two windows (30), and you have about 366 square feet. At 350 square feet per gallon, one coat needs just over one gallon, so two coats need roughly 2.1 gallons. Buying two gallons plus a quart, or simply three gallons if the color is a custom mix, gives you a safe margin.
Quick Estimates by Room Size
| Room | Approx. wall area | Two-coat gallons |
|---|---|---|
| Small bathroom (5 x 8 ft) | About 170 sq ft | 1 |
| Bedroom (10 x 12 ft) | About 300 sq ft | 2 |
| Bedroom (12 x 14 ft) | About 366 sq ft | 2 to 3 |
| Living room (15 x 20 ft) | About 520 sq ft | 3 |
These are estimates with 8 foot ceilings, so adjust them for your own measurements. If you are asking how much paint do I need for a ceiling too, calculate the floor area (length times width) and treat it as a separate surface.
Things That Change How Much Paint You Use
Surface Texture and Porosity
Rough, textured or unprimed walls soak up more paint, so coverage per gallon drops. New drywall can absorb a lot, which is why primer is worth considering. Our article on whether you need primer explains when it pays off.
Color Change
Going from dark to light, or covering a bold shade, may need a third coat. Going from similar to similar might manage with one and a half. Deep, saturated colors often need extra coats too.
Application Method
Sprayers tend to use more paint than rollers because of overspray and a heavier film. Compare the two in paint sprayer vs roller before you decide.
Smart Buying Tips
If a project needs more than one gallon, combine cans in a large bucket so the color stays uniform; this is called boxing. Ask the store to tint all the paint from the same batch. Keep the unopened leftover can, since a sealed can lasts longer. See our guide to storing leftover paint to keep it usable. Still wondering how much paint do I need for trim? A quart is usually plenty for an average room’s baseboards and door casings. For general background on the material itself, see paint on Wikipedia.
When you know how much paint do I need, it becomes a simple shopping list. Compare the answer against the label for your chosen paint, and when in doubt, round up.
Safety Note
Open windows and run a fan so fresh air moves through the room while you work and while the paint dries. If your home was built before 1978, the existing paint may contain lead. Use a lead test kit before sanding or scraping, and follow EPA-recommended lead-safe work practices if the result is positive. Never dry-sand suspect paint.
Frequently Asked Questions
How much paint do I need for a 12×12 room?
With 8 foot walls that is about 384 square feet before subtracting openings. Two coats usually come to about two gallons, depending on the paint’s coverage.
How many square feet does a gallon of paint cover?
Most labels say roughly 350 to 400 square feet per gallon, but check your specific can because coverage varies by product and surface.
Do I need to include the ceiling in my calculation?
Only if you are painting it. Treat it as its own surface by multiplying room length by width, then use the same coverage rule.
Should I buy extra paint?
A small surplus is wise for touch-ups, and it keeps the exact color on hand. Store it sealed and label it with the room and date.
Does a primer reduce how much paint I need?
On porous or new surfaces, primer seals the wall so your topcoat covers better and often needs fewer coats.
