How Many Square Feet Does a Gallon of Paint Cover? Coats, Primer and Room Examples

A gallon of paint covers about 350 to 400 sq ft per coat on smooth walls by Sherwin-Williams’ SuperPaint data sheet, and 400 to 450 sq ft by Benjamin Moore’s Regal Select page. Divide wall area × coats by that figure.

A 12 × 14 ft room with 8 ft walls, one door and two windows has 372 sq ft of wall. Two coats at 350 sq ft per gallon is 2.126 gallons, so buy 3 gallons, or 9 quarts if you buy by the quart.

How many square feet does a gallon of paint cover?

It is stated per product, so it changes with the paint you pick. These are the manufacturer figures we could check, per gallon and per coat:

The Behr row is lower confidence: we could not open Behr’s page and the range comes from a search summary of it, so check the can. It shows how wide a manufacturer’s range can be. For a generic estimate, 350 sq ft per gallon is the low end of the Sherwin-Williams range, and so a cautious planning figure. Always replace it with the number on the can you buy.

The “mils” in the Sherwin-Williams basis are thousandths of an inch of wet film. A gallon is 231 cubic inches, so at 4 mils (0.004 in) it spreads over 231 ÷ 0.004 = 57,750 sq in, or 401 sq ft, before any loss. That is why the top of the printed range sits near 400 and the bottom is the safer planning number.

How do you calculate how much paint you need?

wall area (sq ft) = room perimeter (ft) × wall height (ft) − doors − windows
paint area        = (wall area + ceiling area, if painted) × coats
gallons           = paint area ÷ coverage (sq ft per gallon)
buy               = round gallons up to the next can size
                    (1 gallon = 4 quarts)

1. Measure each wall’s width and the height. The room perimeter is 2 × (length + width) for a rectangular room.
2. Multiply the perimeter by the wall height, and subtract openings. A typical interior door is about 20 sq ft (3 ft × 6 ft 8 in) and a typical window about 12 sq ft (3 ft × 4 ft). These are nominal sizes, so use your own measurements. Baseboards and trim are not included, so add their area if you will paint them.
3. Add the ceiling (length × width) if it gets the same paint.
4. Multiply by the number of coats. Two coats is the usual plan.
5. Divide by the coverage from the can.
6. Round up to a can size you can buy. A quart is 1/4 gallon, so you can buy 2.25 gallons as 9 quarts.

The square footage calculator works out odd-shaped walls, and the drywall calculator finds room wall area and takes openings into account. Both give you the area to put in the formula, or the paint calculator runs the whole formula for you.

Worked example: a 12 × 14 ft room

• Perimeter: 2 × (12 + 14) = 52 ft. Wall area: 52 × 8 = 416 sq ft.
• Openings: one door (20 sq ft) and two windows (2 × 12 = 24 sq ft). Net wall: 416 − 20 − 24 = 372 sq ft.
• Two coats: 372 × 2 = 744 sq ft of paint area.
• At 350 sq ft per gallon: 744 ÷ 350 = 2.126, so 3 gallons, or 2.25 gallons as 9 quarts.
• At 400: 744 ÷ 400 = 1.86, so 2 gallons. At 450: 744 ÷ 450 = 1.653, so 2 gallons, or 1.75 as 7 quarts.
• Primer, one coat at 400: 372 ÷ 400 = 0.93, so 1 gallon.
• Ceiling, 12 × 14 = 168 sq ft, two coats: 336 ÷ 350 = 0.96, so 1 gallon.

The range from 2 to 3 gallons for the same room shows why the coverage figure matters. If the result lands close to a gallon line, round up or add a quart.

Quick table: gallons for common rooms

Walls only, 8 ft ceiling, no door or window deducted (so these run slightly high), two coats, whole gallons rounded up.

What changes how far paint goes?

• Surface. Rough, porous or textured walls and new, unprimed drywall soak up more paint than smooth, previously painted ones. Behr states that its range depends on texture and porosity.
• Color change. Going from a dark color to a light one often needs more coats than the usual two.
• Application. Behr states that its range depends on the application method, so check the data sheet for the product and how you will apply it.
• Coats. Two is a common plan. The coverage figure is per coat, so a third coat adds another full pass.

Plan for the low end of the range on rough or porous surfaces and when changing color strongly.

Do you need primer, and how far does it go?

Primer is a separate coat with its own coverage. Sherwin-Williams lists 400 sq ft per gallon for its Premium Wall & Wood primer at 4 mils wet, and one coat is the usual plan. New drywall, bare patches and stains are typical places for it, but the paint label says when its product needs it, and the primer’s label gives its coverage. Count primer area separately: the net wall area is divided by the primer’s coverage, not the paint’s.

Assumptions and limits

• Coverage figures are the manufacturers’ own, for the products named, on smooth surfaces. They are not guarantees. Your can is the authority.
• No prices are quoted here. Prices vary by brand, sheen and store, so check them with the retailer.
• Standard door and window sizes are nominal defaults. Measure the openings in your room.
• For homes built before 1978, lead-safe work practices apply to surface preparation. The EPA has rules for this, and the estimate does not account for it.

Common questions