TOOL 02 / FREE · NO SIGNUP
Area & Room Calculator
Measure a floor or one room. Subtract doors and windows once, then reuse the result.
Worked example loaded. These are example measurements and product assumptions.
THE METHOD
How to use this estimate
- For a floor, use the measured inside dimensions. The triangle option uses a perpendicular height; circles use diameter.
- Full room mode adds wall height. Door and window counts are whole numbers; each counted opening needs width and height.
- Ceiling area equals floor area for a flat rectangular room. Sloped ceilings and irregular walls need separate measured areas.
floor = length × width; net walls = 2 × (length + width) × height − openings
A worked example
The “Load worked example” button uses the same inputs as this example. Explicit unit suffixes keep their meaning in either unit system.
- How will you measure?
- Full rectangular room
- Length
- 12 ft
- Width / perpendicular height
- 15 ft
- Room height
- 9 ft
- Doors
- 1
- Door width
- 3 ft
- Door height
- 7 ft
- Windows
- 2
- Window width
- 4 ft
- Window height
- 5 ft
- Net wall area
- 39.484 m² / 425 ft²
- Gross walls
- 45.151 m² / 486 ft²
- Openings
- 5.667 m² / 61 ft²
- Ceiling
- 16.723 m² / 180 ft²
- Perimeter
- 16.459 m / 54 ft
- Room volume
- 45.873 m³ / 1,620 ft³
Questions, answered
Can I use a known area?
Choose “I know the area” to skip dimensions.
What can I reuse in Project Lite?
A rectangular room’s length, width, height and openings can be carried to Paint and Project Lite. Floor area can be sent to Flooring and Tile.
Sources and product assumptions
These references explain units or product specifications. Your selected product label takes priority; none of these sources endorses this calculator.
Source check: 4 October 2026. Worked examples use stated, editable assumptions.