Quick answer
Calculate gross wall area from room perimeter multiplied by wall height, subtract major openings, multiply by coats and divide by the product coverage rate.
Step by step
- Measure the room. Add wall lengths to find perimeter.
- Calculate wall area. Multiply perimeter by wall height.
- Subtract openings. Remove large doors and windows when useful.
- Apply coats and coverage. Round to the available can size.
Formula or rule of thumb
Example
A room with 352 ft² of gross wall area, 30 ft² of openings and two coats has 644 ft² of coat-area before dividing by product coverage.
Common mistakes
Do not use floor area as wall area, and do not assume every paint product has the same coverage.
Planning note: product yields, installation methods, site conditions and local requirements can change the final quantity. Use the exact manufacturer or supplier information before purchasing.
FAQ
Should I include the ceiling?
Estimate the ceiling separately.
Do dark colors need more paint?
They may require additional coats or primer depending on the existing color and product.
Should I buy extra?
Keep a small amount for touch-ups, but follow the retailer's return policy for unopened cans.