GUIDE · 2026-07-23
How to use the Room Area & Paint Calculator
This calculator keeps floor, ceiling and four-wall area separate. It subtracts openings, applies coats and label coverage, then distinguishes exact paint need from whole-container purchasing.
How it works
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Step-by-step
- 01Choose U.S. or metric units and measure room length, width and height.
- 02Enter unpainted door and window area, coats and the coverage printed on the paint label.
- 03Compare exact paint, whole-container purchase, flooring allowance and optional cost.
Worked example
INPUT12×10×8 ft room; 36 ft² openings; 2 coats; 350 ft²/US gal
RESULT316 ft² paintable wall; about 1.81 US gal → two 1-gallon cans
A porous surface or dramatic color change may require more product than the geometric estimate.Limits and checks
- A U.S. gallon is not an Imperial gallon; English defaults use U.S. gallons.
- Columns, slopes and built-ins are not automatically represented by the rectangular-room formula.
Useful examples
- Estimate paint before a DIY project
- Calculate flooring order area with waste allowance
- Compare a room in metric or US customary units
Frequently asked questions
Is ceiling paint included?
The main paint result covers walls only. Ceiling area is shown separately.
What does coverage mean?
It is the area one liter or gallon covers for one coat. Use the value printed on your paint label.
Can the purchase amount differ?
Yes. Wall condition, tools, losses and irregular geometry affect real use, so treat this as a planning estimate.