Quick answer
Measure each wall elevation, calculate gross area, subtract meaningful openings and divide coat-area by the exact product coverage. Rough siding and masonry usually need more careful allowance than smooth surfaces.
Step by step
- Measure elevations Record length and height for each wall plane.
- Subtract major openings Remove large doors and windows.
- Assess surface Texture, porosity and previous color affect coverage.
- Calculate coats Use primer and finish product coverage separately.
Formula or rule of thumb
Example
A 1,200 ft² exterior with 2 coats and a 350 ft²/gal product has 6.86 theoretical gallons before rounding and surface allowance.
Common mistakes
Using floor area, assuming smooth-wall coverage on rough siding, and forgetting trim, soffits or separate colors.
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 trim be separate?
Yes, trim usually uses a different product and coverage rate.
Does masonry need more paint?
Porous masonry can absorb more coating; follow the product system.
Should primer be included?
Include primer as a separate coat and product.