Paint Cost Calculator: Gallons, Coats, and Price

How the paint cost calculator works

Four moves: perimeter times ceiling height for gross wall area, subtract the openings, multiply by coats, divide by coverage and round up to whole gallons.

The calculator uses the Sherwin-Williams basis for openings: a 3 by 7 ft door is 21 sq ft, a 3 by 5 ft window is 15. A door and two windows remove 51 sq ft.

Coverage comes from the manufacturers. Sherwin-Williams plans at 350 sq ft per gallon and rounds up; Benjamin Moore lists 350 to 400 for Aura and 400 to 450 for Regal Select and ben. This page figures at 350, the conservative end.

Worked example: a 12 by 12 bedroom

Perimeter is 48 ft. At an 8 ft ceiling that is 384 sq ft of gross wall. One door and two windows deduct 51, leaving 333 sq ft to paint. Two coats make it 666.

Divide by 350 and round up: 2 gallons. In the mid tier, Regal Select to Duration Home list prices, the paint runs $157.98 to $191.98. Paint only; prep and labor are separate lines.

SimplyWise Cost Estimator prices all of those lines from a photo in about 6 seconds.

Common rooms at a glance

All rows: 8 ft ceiling, one door, two windows, two coats, mid tier band.

At 9 ft the same room carries 381 sq ft, and two coats tip in a third gallon.

What a gallon of paint really costs

Two makers publish national list prices, both captured August 27, 2026. Benjamin Moore: ben $60.99, Regal Select $78.99 to $84.99 by sheen, Aura $108.99. Sherwin-Williams: SuperPaint $83.49, Duration Home $95.99, Emerald $101.49 per gallon.

Each band blends both makers: Good spans ben to SuperPaint, Better Regal Select to Duration Home, Best Emerald to Aura. Contractor accounts, sales, and big box house brands land under list; treat the bands as the walk-in ceiling.

Coats, coverage, and the labor line

Two coats is the working default and doubles the area. One coat holds up only on a close color over sound paint; a drastic change or fresh drywall can push a third, plus primer.

Labor is deliberately not a line here. No national source publishes an honest per square foot painting rate. For scale, BLS puts the median painter wage at $23.75 an hour, May 2025; a shop bills well above its wage. Get labor from a local bid, not a national table.

Run the estimate in this order

1. Measure the walls, not the floor

   The floor plan says 144 sq ft; the walls you are painting say 384.

2. Count the openings

   Every door is 21 sq ft you do not paint, every window 15. Skip the deduction and you buy an extra gallon.

3. Pick the tier before you price

   The spread between ben and Aura is $48 a gallon. Tier first, then the dollars mean something.

4. Put the whole job on paper

   Paint is one line. Prep, patching, primer, labor, and cleanup are the rest of the estimate the customer signs.