Measure each wall first
Record every relevant dimension in the same unit and separate irregular sections. Small measuring errors multiply across an entire project, so check each figure before adding a waste allowance.
Coverage and coats
Coverage on the tin is normally stated per litre for one coat. Multiply the paintable area by the number of coats, then divide by the stated coverage. Porous, textured or strongly contrasting surfaces may need more.
Turn the result into a buying quantity
Calculations produce a net requirement, while shops sell fixed packs. Round up only at the final buying step, compare pack coverage, and keep unopened paint returnable where the retailer permits it.
Practical checklist
- Subtract doors and windows only when they are substantial.
- Keep a little of the final mixed colour for touch-ups.