Skip to content
Home

Paint Calculator

Paint Calculator

Estimate how much wall paint you need from room size, coats, coverage, and openings.

Results update as you type.

How to use

Enter room length, width, and height in feet. Adjust doors, windows, coats, coverage (from the paint can), and waste. Buy the rounded-up gallon count.

Formula

wall_area = 2 × (length + width) × height
paintable = wall_area - (doors×21 + windows×15)
needed_sqft = paintable × coats × (1 + waste/100)
gallons = needed_sqft / coverage

Worked examples

  1. 12×10×8 ft room, 1 door, 2 windows, 2 coats, 350 sq ft/gal, 10% waste → about 1.89 gal (buy 2).
  2. 10×10×8 ft room, no openings, 1 coat, 350 coverage, 0% waste → 320 ÷ 350 ≈ 0.91 gal (buy 1).

Assumptions

  • Four walls only. Ceiling and trim are not included.
  • Default door area 21 sq ft and window 15 sq ft (common DIY rules of thumb); adjust by changing counts or coverage.
  • Default coverage is 350 sq ft per gallon. Always prefer the number printed on your paint can.
  • Estimates assume rectangular rooms and average surface porosity. Textured walls may need more paint.

FAQs

Should I paint the ceiling with this estimate?
No. Add length × width separately for the ceiling, or use a dedicated ceiling calculation.
Metric rooms?
Convert metres to feet first (1 m ≈ 3.281 ft), or convert coverage to sq m per litre consistently.
Why round up gallons?
Paint is sold in whole cans. Rounding up avoids a second trip and covers touch-ups.

Related tools