How to use this calculator
Measure your room length, room width and consistent wall height using the same length unit. Add the count and average dimensions of doors and windows that should be excluded. The result shows both square feet and square metres.
The calculation explained
Gross area = 2 × (room length + room width) × wall height. Opening area = window count × window width × window height + door count × door width × door height. Net area = gross − openings.
Check these details before ordering
- Measure each wall separately for irregular rooms, alcoves or inconsistent wall heights.
- Only subtract openings that you will not coat.
- Measure actual trim or ceiling exclusions if the finish design requires them.
Frequently asked questions
Does this work for irregular rooms?
Not directly. Measure each wall in sections and add the areas manually. Our measuring guide explains this method.
Should I subtract every window and door?
Subtract only openings that will not be coated. Account separately for returns or reveals you intend to finish.
Will switching units convert my existing numbers?
No. The unit selector changes how the typed measurements are interpreted. Enter converted values when switching systems.
Read the related guide
For more context, see How to Measure Walls Before Ordering Decorative Finishes. It explains practical assumptions that a calculator cannot confirm for your individual project.