How to Measure a Room for Paint and Avoid Buying Too Much

Measure each surface separately

Measure the length and height of every wall, then multiply them to find area. Add the wall areas together. Measure ceilings as length multiplied by width. Keeping walls, ceilings and woodwork separate helps when they use different products or colours.

Subtract only large openings such as wide windows or double doors. Leaving small openings in the total provides a useful allowance for touch-ups and uneven coverage.

Account for coats and coverage

The coverage printed on the tin is a guide under suitable conditions. Porous plaster, textured walls, strong colour changes and inexperienced application can reduce it. Multiply the surface area by the number of planned coats before dividing by the stated coverage rate.

Primer is not automatically interchangeable with finish paint. New plaster, stains, bare wood and difficult surfaces may need a specific preparation system.

Buy consistently

Purchase enough finish paint from the same batch where possible, especially for large uninterrupted walls. Slight colour differences may be visible when separate batches meet. Keep a small labelled amount for later repairs.

Check whether the supplier allows unopened tins to be returned. That can make a sensible small over-order less risky while avoiding a shortage halfway through a coat.

Preparation changes the budget

Include filler, abrasives, masking, caulk, dust sheets, rollers, brushes and cleaning products. Repairing cracks or damp is not the same as hiding them with paint. Solve the cause of damage before decorating.

High ceilings, suspected lead paint, active damp and badly damaged plaster are good reasons to seek professional advice.

Project checklist

• ✓ Measure every wall
• ✓ Calculate ceilings separately
• ✓ Multiply by number of coats
• ✓ Check product coverage
• ✓ Allow for primer and preparation
• ✓ Keep paint for touch-ups