Property Repair Calculators

Paint Calculator

A gallon of interior wall paint covers roughly 350 to 400 sq ft per coat, depending on the product. [1] Measure your walls, subtract doors and windows, and multiply by the number of coats to get how many gallons, quarts, or 5-gallon buckets to buy.

Results

Paint to buy

2.25 gal

2 gal + 1 qt · exact need 2.19 gal

Wall area: 416 sq ft
Doors and windows: −33 sq ft
Area to paint: 383 sq ft
Paint (2 coats): 2 gal + 1 qt

Rough, porous, or bare surfaces and big color changes use more paint. Buy the fewest containers that cover the quart-rounded amount; a 5-gal bucket is only suggested once you need 5 gallons or more.

How this was calculated

Walls = 416 sq ft
Openings = 33 sq ft
Net walls = 416 − 33 = 383 sq ft
Paint = 383 × 2 coats ÷ 350 = 2.19 gal
Rounded up to the quart: 2.19 → 2.25 gal = 2 gal + 1 qt

Worked example

A 12 × 14 ft bedroom with 8 ft walls, one 3 × 7 ft door, and one 3 × 4 ft window, painted with two coats at 350 sq ft per gallon.

Walls:   2 × (12 × 8) + 2 × (14 × 8) = 416 sq ft
Openings: 3 × 7 + 3 × 4 = 33 sq ft
Net:     416 − 33 = 383 sq ft
Paint:   383 × 2 ÷ 350 = 2.19 gal
Buy:     2.19 → 2.25 gal = 2 gal + 1 qt
Primer:  383 × 1 ÷ 400 = 0.96 → 1 gal

How the formula works

area to paint = wall area − doors and windows (+ ceilings)
gallons       = area to paint × coats ÷ coverage per gallon
to buy        = gallons rounded up to the next quart (¼ gal)
containers    = 5-gal buckets, then gallons, then quarts

Rounding happens once, at the end, to the nearest quart, because that is the smallest can most stores sell. The quart-rounded total is then split into the fewest containers: 5-gallon buckets first, then gallons, then quarts. For example, 6.3 gallons rounds to 6.5 gallons, which is one 5-gallon bucket, one gallon, and two quarts.

Limitations

Coverage on the can assumes a smooth, sealed surface at the manufacturer’s film thickness. Bare drywall, textured walls, masonry, and dark-to-light color changes can use noticeably more.
Doors and windows are measured as rectangles. Trim, cabinets, and built-ins are not subtracted unless you add them as openings.
Trim, doors, and ceilings in a different product or sheen need their own estimate.
Primer is estimated as one coat over the same area. Some surfaces need spot priming only; others need a stain-blocking or masonry primer with a different coverage rate.
Paint within the same color can vary slightly between batches. Buying one extra quart or mixing cans together (boxing) is a common way to avoid a visible difference.

Common scenarios

Repainting after a water or drywall repair: new drywall compound is porous. Add a primer coat over patched areas so the finish sheen matches the rest of the wall.
Dark color over light (or the reverse): Behr says a deep, intense color may need more coats or a tinted primer. [2] Try 3 coats or add primer to see the difference.
Whole room including the ceiling: add the ceiling under “Ceilings” only if it gets the same paint. Ceiling paint is usually a separate flat product.
Checking a contractor’s material line: enter their square footage as one wall with a height of 1 ft, set their number of coats, and compare gallons.

Common questions

How many square feet does a gallon of paint cover?

It depends on the product and surface. Sherwin-Williams lists 350–400 sq ft per gallon for SuperPaint Interior Latex Satin, and Behr says a gallon of its paint covers 250–400 sq ft with one coat. Use the coverage on your can.

Do I need two coats of paint?

Often, yes. Sherwin-Williams’ SuperPaint data sheet specifies two coats over drywall, and Benjamin Moore’s primer sheet calls for one or two finish coats over primer. A second coat evens out color and sheen.

Should I subtract doors and windows?

Yes, for an accurate count. This calculator subtracts every opening you enter. If you skip them, the extra paint acts as a waste allowance.

Is it cheaper to buy a 5-gallon bucket?

Often per gallon, but this calculator only suggests a bucket when you need 5 gallons or more. It doesn’t use prices, so check your store’s per-gallon cost.

How much primer do I need?

Primer covers a different area per gallon. Benjamin Moore lists 400–450 sq ft per gallon for Fresh Start Multi-Purpose Latex Primer. This calculator assumes one primer coat over the same area as the paint.

Sources and methodology

Coverage defaults are manufacturer figures for specific products, used as editable starting points. They are not a standard for every brand. This page is quantity only: it uses no prices.

[1] Sherwin-Williams — SuperPaint Interior Latex Satin (A87) product data sheet. Retrieved 2026-09-25. Sherwin-Williams SuperPaint Interior Latex Satin: “Coverage: 350-400 sq. ft. per gallon @ 4 mils wet 1.5 mils dry.” The low end is the default so the estimate does not come up short. The SuperPaint data sheet’s drywall system is 2 coats of the finish (self-priming) or 1 coat of primer plus 2 finish coats. Benjamin Moore’s Fresh Start sheet lists “1 or 2 coats” of finish over the primer.
[2] Behr — How much paint do I need?. Retrieved 2026-09-25. Behr: “One gallon of any BEHR paint is enough to cover between 250 to 400 square feet of surface area with one coat.” Deep colors may need more coats or a tinted primer.
[3] Benjamin Moore — Fresh Start Multi-Purpose Latex Primer (N023) technical data sheet. Retrieved 2026-09-25. Benjamin Moore Fresh Start N023: “Coverage per Gallon at Recommended Film Thickness 400 – 450 Sq. Ft.,” depending on surface texture and porosity. Low end used as the default.

This tool provides an educational estimate only. Insurance companies, contractors, and building officials may calculate these figures differently depending on policy language, property condition, local pricing, and applicable codes.

Disclaimer: Calculators and information on this site are provided for educational and estimating purposes only. Results do not determine insurance coverage, claim payments, repair requirements, or professional recommendations.