Updated October 2026
Painting calculators and cost guides
Painting is the cheapest major upgrade you can make to a room, and the easiest one to overspend on — most people buy 20–30% more paint than the job needs because nobody worked out the wall area first.
Start with the calculator
- Paint calculator Enter room dimensions, doors and windows, and coats. Get gallons, cost and a paintable area figure.
Cost guides
- How much does it cost to paint a house? Interior and exterior ranges by square footage, DIY vs professional, and what actually drives the price.
- How much does a gallon of paint cover? The 350 sq ft rule, when it is wrong, and how surface texture changes your estimate.
Quick numbers before you start
| Item | Typical figure |
|---|---|
| Standard interior door | ~21 sq ft of wall area |
| Standard window | ~15 sq ft of wall area |
| Coverage, 1 gallon | 350–400 sq ft per coat |
| Coats for a color change | 2 (3 if going light over dark) |
| Pro interior painting | $2–$6 per sq ft of floor area |
A quart covers roughly 100 sq ft. If your gallon count comes out at 3.2, buy 3 gallons and a quart — not 4 gallons.