Show the formula and working
This free spray paint coverage calculator tells DIYers and upcyclers in the UK, Ireland and Europe how many aerosol cans they need to spray a panel, a piece of furniture, a pipe or rail, or any surface whose area they know. Enter the size, the number of items and coats, and the coverage printed on the can, and it adds an overspray allowance and rounds up to whole cans.
Quick answer: A spray paint coverage calculator multiplies the area by the number of coats, adds an overspray allowance and divides by the coverage per can. A 400 ml aerosol typically covers about 1.5 m² per coat, so 1 m² with two coats and 15% allowance needs 2.3 m² of coverage, which is 2 cans.
What Is a Spray Paint Coverage Calculator?
A spray paint coverage calculator is a tool that turns the size of the thing you are spraying into the number of aerosol cans to buy.
The formula in plain words: first find the area of one item. A flat panel is length times width, doubled if you spray both sides. A box or cabinet adds the top, the front and back, and the two ends. A round pipe, rail or leg is 3.1416 times the diameter times the length. Multiply by the number of items and the number of coats. Add the overspray and waste allowance as a percentage, because some paint always misses the surface. Divide the total by the coverage per can and round up to a whole can.
How Do You Use the Spray Paint Coverage Calculator?
- Choose the Shape that best matches the item: flat panel, box or cabinet, round pipe, or I know the area.
- Enter the Length, plus the Width, Height or Diameter the shape needs, or type the Area directly.
- For flat panels, set Sides to paint. Then enter the Number of identical items and the Coats.
- Copy the Coverage per can and the Can size from the label or the maker’s data sheet.
- Adjust the Overspray and waste allowance: keep it low for big flat panels indoors and raise it for railings, mesh or windy days.
- Read the number of cans in the result, then open “Show the formula and working” to see the area and each step.
How Much Does One Can of Spray Paint Cover?
One 400 ml can of spray paint covers roughly 1 to 2 m² per coat, depending on the product and the colour. The PlastiKote data sheet for its fluorescent spray gives 1.5 m² for a 400 ml can, a PlastiKote metal paint and primer is listed at up to 1.75 m² per can, and the Rust-Oleum Painter’s Touch 2X data sheet gives 8 to 12 square feet (about 0.74 to 1.11 m²) for a 12 oz can. Always use the figure on your own can, because coverage per can is the number that drives the result.
How Many Cans of Spray Paint Do You Need for a Piece of Furniture?
A small chest of drawers or bedside table usually needs 3 to 4 cans for two coats, because the outside faces add up faster than people expect. A chest 0.8 m long, 0.4 m deep and 0.9 m high has 2.48 m² of outside faces without the base. Two coats plus 15% allowance make 5.7 m², which is 4 cans at 1.5 m² each. Drawer fronts and legs are already part of those faces, but open shelves and the inside of drawers add more.
How Much Spray Paint Is Lost to Overspray?
Overspray depends on the shape more than the paint: a solid flat panel wastes little, while railings, mesh and thin legs waste much more because most of the spray passes through the gaps. That is why the calculator uses an editable allowance rather than a fixed figure. Spraying in several thin coats from the distance on the can, often 25 to 30 cm for PlastiKote, keeps runs and waste down. For long runs of fence panels or railings, a brush or roller with tinned paint is usually cheaper; the fence paint calculator sizes that job in litres.
How Long Should You Wait Between Coats of Spray Paint?
Follow the recoat window on the can, which for many enamel aerosols is within 1 hour or after 48 hours. Rust-Oleum gives exactly that window for Painter’s Touch 2X, with touch dry in 20 minutes and application between 10 and 32°C at humidity below 65%. Recoating between those times can make the first coat wrinkle as the solvents in the second coat lift it.
Spray Paint Coverage Reference Table
Cans needed for two coats with a 15% overspray allowance, at two common coverage figures.
| Area (one coat) | Total with 2 coats and 15% | Cans at 1.5 m² per can | Cans at 1 m² per can |
|---|---|---|---|
| 0.25 m² | 0.58 m² | 1 | 1 |
| 0.5 m² | 1.15 m² | 1 | 2 |
| 1 m² | 2.3 m² | 2 | 3 |
| 2 m² | 4.6 m² | 4 | 5 |
| 3 m² | 6.9 m² | 5 | 7 |
| 5 m² | 11.5 m² | 8 | 12 |
Worked Example: Spraying a Chest of Drawers
Example: a chest of drawers being upcycled is 0.8 m long, 0.4 m deep and 0.9 m high. Choose Box or cabinet, 5 outside faces (no base) as the Shape, enter the three sizes, keep 2 Coats, 1.5 m² Coverage per can, 400 ml cans and a 15% allowance.
- Area: top 0.32 m² + front and back 1.44 m² + two ends 0.72 m² = 2.48 m².
- Area to spray: 2.48 m² x 2 coats = 4.96 m².
- With allowance: 4.96 m² x 1.15 = 5.7 m².
- Cans: 5.7 / 1.5 = 3.8, rounded up to 4 cans of 400 ml.
If you later paint the walls behind it, the paint calculator works out the emulsion for the room.
Spray Paint Coverage Calculator FAQs
How many square metres does a 400 ml spray can cover?
A 400 ml spray can covers about 1 to 2 m² per coat. PlastiKote gives 1.5 m² for its 400 ml fluorescent spray and up to 1.75 m² for its metal paint and primer. Light colours over dark surfaces need more coats, so use the label figure and your real number of coats.
How many coats of spray paint should I apply?
Most jobs need two light coats, and makers advise several thin layers rather than one heavy coat, which runs. Add a primer coat on bare metal, plastic or wood unless the can says it is a paint and primer in one. A big colour change may need a third coat.
Is spray paint cheaper than brush paint?
Spray paint usually costs more per square metre than tinned paint, because a 400 ml aerosol covers only about 1.5 m². It saves time and gives a smooth finish on small, fiddly items such as chairs, frames and metal fittings. For large flat areas, a brush or roller is normally cheaper.
What temperature is best for spray painting?
Most aerosols work best in mild, dry weather. PlastiKote gives a best working temperature of 10 to 25°C, and Rust-Oleum gives 10 to 32°C with humidity below 65%. Cold cans spray unevenly, so keep them indoors before use, and avoid spraying in damp or windy conditions.
How do I work out the area of a chair or railing?
Break it into simple shapes. Treat each leg or bar as a round pipe (length times diameter times 3.1416) and each seat or back as a flat panel. Add the areas, or enter the total with the I know the area option, and raise the overspray allowance for open frames.
Is it safe to use spray paint indoors?
Spray outdoors or in a very well ventilated space, because aerosol paints contain solvents and propellant that are harmful to breathe and highly flammable. Keep away from flames and heaters, wear a suitable mask and follow the safety advice on the can. Cover nearby surfaces to catch overspray.
More tools for brush and roller jobs are in the paint and decorating calculators. For background on how aerosol paint works, see the Wikipedia article on aerosol paint.
Checked October 2026. Sources: PlastiKote fluorescent spray paint data sheet (European Aerosols), Painter’s Touch 2X Ultra Cover data sheet (Rust-Oleum), PlastiKote Metal Paint and Primer 400 ml product listing.