Spray paint gives a smooth finish on metal, wood, plastic and wicker without brush marks, but a lot of it ends up in the air rather than on the object. This calculator estimates the cans of color and primer for a project, with an allowance for overspray.
Coverage of a can
A standard 12 oz aerosol can covers about 20 to 25 sq ft per coat on a smooth, flat surface. Coverage drops sharply on:
- open shapes such as chairs, railings, wicker and lattice, where much of the spray passes through;
- rough or porous surfaces such as raw wood, concrete and cast iron;
- dark-to-light color changes, which need more coats.
How the calculation works
- Cans of color = area × coats × (1 + overspray) ÷ coverage per can, rounded up
- Cans of primer = area × (1 + overspray) ÷ coverage per can, if you prime
- Plan 20% overspray for flat panels and 50% or more for open objects
Example
Two coats on 50 sq ft of surface, with 20% overspray and 20 sq ft per can, take 50 × 2 × 1.2 ÷ 20 = 6 cans. A primer coat would add 3 cans.
Estimating the surface
- Flat panel or tabletop: length × width, for each face you paint.
- Cylinder (legs, pipes): π × diameter × length.
- Chair: count each slat and leg; a dining chair is often 10 to 15 sq ft of surface.
- When in doubt, buy one extra can of the same batch: colors can vary slightly between batches.
Tips for a smooth finish
- Clean, degrease and sand glossy surfaces lightly; remove rust with a wire brush.
- Use a primer suited to the material: metal primer, plastic adhesion promoter or a stain-blocking primer on wood.
- Shake the can for a full minute after the ball starts rattling, and again often.
- Spray from 8 to 12 in away in steady, overlapping passes, starting and stopping beyond the edge of the object.
- Apply several light coats rather than one heavy one, which runs and drips.
- Respect the recoat window on the can: either within an hour or after 48 hours for many enamels.
Spray outdoors or in a well-ventilated area, with a respirator rated for organic vapors, at temperatures between about 50 and 90 °F and low humidity, away from flames and sources of ignition.