Paint Calculator for Walls
This paint calculator for walls lets you enter each wall separately instead of assuming a perfect rectangle. Useful for L-shaped rooms, open-concept spaces with partial walls, or a single accent wall. Enter up to four wall lengths plus the common ceiling height and the calculator returns gallons needed, liters, and estimated cost after subtracting doors and windows.
Why a Wall-by-Wall Paint Calculator for Walls?
Most paint calculators assume a rectangle: perimeter x ceiling height. That works for a plain bedroom. It falls apart for:
- L-shaped rooms (the perimeter shortcut counts non-existent walls)
- Open-concept layouts where only two or three walls are being painted
- Accent walls where you paint one wall a different color
- Powder rooms and nooks where one "wall" is actually a mix of half-walls and built-ins
Enter the length of each wall you actually plan to paint (leave the rest at 0). The calculator multiplies each by your common ceiling height, sums them, subtracts door and window openings, and divides by coverage.
Paint Calculator for Walls Formula
Paintable Area = (Wall1 + Wall2 + Wall3 + Wall4) x Height - (Doors x 21) - (Windows x 15)
Gallons Needed = Paintable Area x Coats / Coverage Rate
Default coverage is 350 sq ft per gallon (standard interior latex on primed drywall). For textured walls, drop to 250; for one-coat premium paint, bump to 400.
Standard Openings
| Opening | Area | Notes |
|---|---|---|
| Standard interior door | 21 sq ft | 6'8" x 3' |
| Standard entry door | 28 sq ft | 6'8" x 4' |
| Standard window | 15 sq ft | 3' x 5' |
| Picture window | 30-60 sq ft | Measure directly |
| Sliding glass door | 50 sq ft | 6'8" x 7'6" |
If your openings are much larger or smaller than standard, measure each individually, total the area, and divide by 15 (or 21) to get an equivalent count to enter.
Accent Wall Example
A single 12 ft accent wall with 8 ft ceilings is 96 sq ft. At 350 coverage and 2 coats: (96 x 2) / 350 = 0.55 gallons. Buy a 1-quart sample pot and a 1-gallon can, and you will have plenty for touch-ups.
Full Bedroom Example
A 14 x 12 bedroom with 8 ft ceilings:
- Walls: 14 + 12 + 14 + 12 = 52 linear ft x 8 = 416 sq ft
- Openings: 1 door (21) + 2 windows (30) = 51 sq ft
- Paintable: 365 sq ft
- 2 coats at 350 coverage = 2.09 gallons
- Order 3 gallons for the base coat color and set aside roughly 0.9 gal for touch-ups
Tips for Accurate Wall Measurement
- Measure at the floor, not at chair rail height. Walls with bump-outs or baseboard heaters sit farther out at the floor line.
- Round up to the nearest half foot. Builders work in 6-inch increments and hand-measured walls rarely have sub-inch precision.
- Skip the closet interiors unless you are painting them; most homeowners leave closet interiors as-is.
- If you are painting ceiling and trim separately, use separate calcs. This one is walls only.