Understanding your result
The headline is the paint in fluid ounces or quarts by brush, or the number of spray cans, and the sub-line is the cans to buy. The three figures show the painted surface, the coats and the number of radiators.
The table shows the front face, the factor for the type and the surface of one radiator, the surface of all of them, and the paint or cans. The factor is the important line: it is why a column radiator takes nearly twice the paint of a panel radiator the same size.
Radiators are metal and small, like railings and furniture. The metal railing calculator covers railings and gates with the same brush-or-can choice; the furniture paint calculator covers metal cabinets and tables; and the trim calculator covers the woodwork around them.
How we calculate this
The type factors are site estimates from the geometry: a single panel is about 2.2 times its face (front, back, top and ends), a double-panel convector about 2.4 (its outer faces and the top grille, not the fins inside), a cast-iron column radiator about 4 (each column painted round), and a baseboard cover about 1.3 (the front and the top). Radiator enamels cover about 100 sq ft per quart by brush; aerosols about 15 sq ft per can per coat on a radiator, lower than on a flat panel because much of the spray passes between the columns. The coverage rates table lists them with the other paints.
The trim and quart maths guide explains why small jobs like this are rounded to quarts and fluid ounces, and the drying guide why the heating stays off until the paint has cured.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| Single panel | 2.2 × front face | Site estimate from the geometry |
| Double-panel convector | 2.4 × front face | Site estimate, outer faces only |
| Cast-iron column | 4 × front face | Site estimate, columns painted round |
| Baseboard cover | 1.3 × front face | Site estimate, front and top |
| Brushed enamel | 400 sq ft per gallon (100 per quart) | Radiator enamel labels |
| Spray can | 15 sq ft per 12 oz can per coat | Aerosol labels quote 12–25 on flat surfaces; less on radiators |
| Allowance | 15% by brush | Loss on a small, awkward job |
Assumptions last reviewed October 8, 2026.
The calculator does not model removing radiators from the wall, stripping old lead paint (which in homes built before 1978 is regulated work under the EPA’s RRP rule), or painting the pipes, which are about 0.3 sq ft per foot of a 1 in pipe.
Two worked examples
Four panel radiators by brush
Single panels, 40 in long and 24 in high, two coats.
- Front face: 40 × 24 ÷ 144 = 6.67 sq ft
- Surface: 6.67 × 2.2 × 4 = 58.7 sq ft
- Paint: 58.7 ÷ 400 × 2 × 1.15 = 1.35 quarts, buy two quarts
Three baseboard covers 72 × 8 in with one coat, for comparison, are 15.6 sq ft and about 5.7 fl oz: a half-pint of spray-grade enamel or a single quart.
Six cast-iron column radiators by spray can
30 in long, 26 in high, two coats.
- Front face: 5.42 sq ft; surface: 5.42 × 4 × 6 = 130 sq ft
- Cans: 130 ÷ 15 × 2 = 17.3, so 18 cans
Eighteen cans is the point where a quart of radiator enamel and a long-handled brush becomes the cheaper route, though slower between the columns.
Where to find your inputs
Type. A flat steel panel is a panel; two panels with fins between them is a double convector; ornate cast iron with vertical sections is a column radiator; a low metal cover along the wall is a baseboard heater.
Length and height. Overall, end to end and floor to top.
Method. Brush and mini roller, or spray cans with masking.
Common mistakes
- Painting a hot radiator. The paint dries too fast, smells and can blister.
- Ordinary wall paint. It yellows and cracks on hot metal.
- Painting over rust. Wire-brush and prime the spots first.
- Measuring the face only. The surface is two to four times larger.
- Painting the valves. Mask them; painted valves stick.
- Heating on before cure. Wait the full time on the can.
Questions people ask
- How much paint does a radiator need?
- A 40 × 24 in single-panel radiator has about 6.7 sq ft of front face and about 14.7 sq ft of painted surface with its back, top and ends. Four of them at two coats take about 1.35 quarts of radiator enamel by brush, so two quarts.
- How many spray cans for a column radiator?
- Cast-iron column radiators have about four times their front face to paint. Six radiators 30 in long and 26 in high are about 130 sq ft, which at about 15 sq ft per can per coat takes 18 cans for two coats.
- Can I use ordinary paint on a radiator?
- Not for long. Ordinary wall paint yellows, cracks and smells on hot metal. Use a paint sold for radiators or heat-resistant to at least 200 °F (93 °C), which covers normal hot-water and steam systems.
- Should the heating be on when I paint?
- No. Paint radiators cold, then leave the heating off until the paint has cured for the time on the can. Heat on fresh paint gives off fumes and can discolour it.
- Do I need to prime a radiator?
- Only on bare metal and rust spots, after wire-brushing them, with a rust-inhibiting metal primer. Sound old paint needs only cleaning and a light scuff.
- Do I paint behind a radiator?
- The visible back of a panel radiator, yes, as far as a long-handled radiator brush or a mini roller reaches. The wall behind it is the wall paint calculator's job, and it is easier with the radiator off the wall.