How to Calculate Paint Coverage in Five Simple Steps

Paint coverage in one line

Paint coverage is simple: multiply the room perimeter by the wall height for wall area, multiply by coats for paint area, divide by coverage per gallon for gallons exact, and round up for gallons to buy. A 14 ft by 12 ft room with 8 ft walls and 2 coats is 416 sq ft of wall, 832 sq ft of paint, 2.38 gallons exact at 350 sq ft a gallon, and 3 gallons to buy.

Step 1: Measure the room

Measure the room with a tape, length and width, and the wall height from floor to ceiling. The worked example is 14 ft long, 12 ft wide, and 8 ft high, a standard bedroom size. Measure the walls you will actually paint: a room with a built-in wardrobe paints less wall than its bare dimensions suggest, and a room with a chimney breast paints more, since the breast adds wall on both sides. Measure twice, because every foot of error here is carried through every step that follows.

Step 2: Find the wall area

Find the wall area from the perimeter times the height. The perimeter is twice the length plus the width: 2 × (14 + 12) = 52 ft. Multiply by the height: 52 × 8 = 416 sq ft of wall. That is the area of all four walls together, before doors and windows. If you want a tight order, subtract the door and window areas now: a standard door is about 21 sq ft and a window about 15 sq ft, and a room with both paints noticeably less than 416 sq ft.

Step 3: Multiply by the coats

Multiply the wall area by the number of coats for the paint area. The example uses 2 coats, so 416 × 2 = 832 sq ft of paint. Two coats are the standard for a colour change or a fresh finish over old paint; one coat is a refresh over the same colour, and three coats are a dark wall painted light. Primer on bare plaster is a further pass on top of the coats counted here, so count it separately rather than folding it into the coat number.

Step 4: Divide by the coverage and round up

Divide the paint area by the coverage per gallon, read off your own can, for gallons exact. The example coverage is 350 sq ft a gallon, so 832 ÷ 350 = 2.38 gallons exact. Round up for gallons to buy, because paint is sold by the whole gallon: 2.38 gallons exact means 3 gallons to buy. The leftover third gallon is not waste — it is the touch-up paint for scuffs, and a room repainted without a touch-up can looks patched within a year.

Step 5: Order and keep the leftover

Order the gallons to buy, all in the same batch, and keep the leftover sealed for touch-ups. The example order is 3 gallons, opened two at a time, with the third mostly full at the end. Check the batch numbers match, since two batches of the same colour can differ visibly on a wall. Write the colour code on the leftover can, because a can without a code is a colour nobody can match, and the next touch-up becomes a fresh paint order.

Paint coverage in numbers

Suppose the room is 14 ft long, 12 ft wide, 8 ft high, the coats are 2, and the coverage is 350 sq ft a gallon. Perimeter: 2 × (14 + 12) = 52 ft. Wall: 52 × 8 = 416 sq ft. Paint: 416 × 2 = 832 sq ft. Exact: 832 ÷ 350 = 2.38 gallons. Buy: 3 gallons. The second gallon is fully used, the third gallon is barely touched, and that leftover is the touch-up stock.

Common mistakes

The most common mistake is counting the floor area instead of the wall area, which under-counts a room badly: a 14 ft by 12 ft room has 168 sq ft of floor but 416 sq ft of wall. The second is forgetting the second coat, which halves the order and leaves the room half painted. The third is using a remembered coverage instead of the can label, since primer and dark colours cover less. The fourth is rounding down instead of up, which leaves the last wall short. The fifth is ordering gallons from different batches, which shows as a colour step on the wall.

Worked example, start to finish

A 14 ft by 12 ft room, 8 ft walls, 2 coats, 350 sq ft a gallon. Perimeter: 52 ft. Wall: 416 sq ft. Paint: 832 sq ft. Exact: 2.38 gallons. Buy: 3 gallons. Result: buy 3 gallons in one batch, paint two coats over 416 sq ft of wall, and keep the leftover third gallon, labelled, for touch-ups.

What changes the answer most

The wall height changes the answer most after the room size: moving from 8 ft to 10 ft walls lifts the wall from 416 to 520 sq ft and the paint from 832 to 1040 sq ft. The coats are second: moving from 2 coats to 1 halves the paint to 416 sq ft and the buy to 2 gallons. The coverage is third: moving from 350 to 400 sq ft a gallon drops the exact from 2.38 to 2.08 gallons but leaves the buy at 3 gallons, since rounding up absorbs small coverage gains.

Frequently asked questions