Paint Calculator
Work out how many gallons of paint you need to paint a room.
How to use this paint calculator
Measure the length and width of the floor and the height of the walls. Count the doors and windows. The calculator takes off about 20 sq ft for each door and 15 sq ft for each window. Most interior paints cover 350–400 square feet per gallon, so 350 is a safe default. Check the label on the can you plan to buy.
How many coats do I need?
- One coat: repainting the same or a very similar color with a good-quality paint.
- Two coats: the normal choice, and needed for any noticeable color change.
- Primer plus two coats: new drywall, bare wood, patched walls, or going from dark to light.
The math behind it
Wall area = 2 × (length + width) × height, minus doors and windows. Multiply by the number of coats and divide by the coverage per gallon. Ceiling area is simply length × width.
Example: a 14 × 12 ft room with 8 ft walls has 416 sq ft of wall. Take off one door and two windows and you're left with 366 sq ft. Two coats is 732 sq ft, or about 2.1 gallons. Buy 2 gallons plus a quart, or 3 gallons if you want leftovers for touch-ups.
Tips for buying paint
- Buy all your paint at once so the batch color matches. If you need several cans, mix them together in a bucket ("boxing").
- Textured or porous walls can soak up 10–20% more paint.
- Keep a labeled quart of leftover paint for future touch-ups.
Often used together
Quick answers
How much area does a gallon of paint cover?
Most interior paints cover about 350–400 square feet per coat on smooth walls. Textured or porous walls use more.
How much paint do I need for a 12 × 12 room?
With 8-foot walls, one door and two windows, that's about 335 sq ft of wall. Two coats is just under 2 gallons.
Do I need primer?
Use primer on new drywall, bare wood, patched spots, stains, or when going from a dark color to a light one. For repainting in a similar color, a paint-and-primer product is usually enough.