Spray Paint Can Calculator

How it works

Aerosol cans are rated by the area one can covers in one coat at the film thickness the maker recommends. The calculator multiplies the surface area by the number of coats, adds any overspray allowance, and divides by the coverage of one can. The result is rounded up to whole cans.

Coverage differs a lot between products and is printed on the can or its technical data sheet. Rust-Oleum's data sheet for Stops Rust Custom Spray 5-in-1 enamel (Form ARJ-2528, Rev. 121625) gives 6–10 sq ft per 12 oz can at a dry film of 1.0–2.0 mils per coat, and says that figure already assumes 15% material loss. The default of 8 sq ft is the middle of that range and is editable, since other products state other figures.

Open work such as railings, spindles, wire mesh and chair frames lets much of the spray pass through or drift past, so the overspray allowance adds a percentage to the area. The 10–20% often quoted for that is a rule of thumb, which is why it is an input and starts at zero.

Formula

area to spray = surface area × coats × (1 + overspray ÷ 100)
cans needed   = area to spray ÷ coverage per can per coat
whole cans    = cans needed, rounded up

Example

A 20 sq ft table with two coats is 40 sq ft of spraying. At 8 sq ft per can that is exactly 5 cans.

A 30 sq ft railing with one coat and a 10% overspray allowance is 33 sq ft. At 6 sq ft per can, the low end of the data-sheet range, that is 5.5 cans: 6 whole cans.

Assumptions and limitations

• Coverage per can comes from the label and is taken as constant. Light coats, a primer underneath or a color that hides poorly change the real figure.
• Can size enters only through the coverage figure. The net weight on a can includes propellant, so ounces are not a reliable way to scale coverage between can sizes.
• The overspray allowance is an editable rule of thumb. The Rust-Oleum data-sheet coverage already includes 15% material loss, so a large extra allowance on solid surfaces counts some of that loss twice.
• Surface area is entered as one figure. Measuring every face of an object, including edges, legs and undersides, is the main source of error.
• The result is an estimate. It is not a substitute for the instructions on the can, including its ventilation and temperature limits.

Frequently asked questions