Understanding your result
The headline is the paint for the number of doors and coats you chose, including the allowance, with the cans to buy in the sub-line. The three figures show the total area, the paint for one coat and the cans. The breakdown explains how a door became an area: the face from width times height, the style factor, the number of sides, the edges and the total for all doors.
Doors are a small-quantity job in paint and a large one in hours. One door is well under a quart; a dozen is four gallons sprayed. Because the amounts are small, the rounding matters: four doors come to 1.06 gallons, which buys a gallon and a quart with most of the quart left. If you are also painting the trim, run the trim and baseboard calculator and add the two before buying; a gallon of enamel is cheaper than four quarts.
The style factor is the number to check. Flush doors are 1.0, panel doors 1.15, glazed doors 0.6 because the glass is not painted, and louvered doors 1.6. A door with a few small panels is closer to 1.1; a six-panel colonial with deep mouldings is closer to 1.2. The garage door calculator applies the same idea to larger panels, and the cabinet paint calculator to small ones.
How we calculate this
The face area of a 36 × 80 in door is 2,880 sq in, or 20 sq ft. The style factor scales it for the extra surface of panels or the missing surface of glass. The edges are the two long sides and the top, at the standard 1.75 in door thickness: about 2.4 sq ft on a standard door, which is roughly a tenth of a face and is split in half when only one side is painted, because then you usually paint the edges that show from that side. In metric the same arithmetic runs in centimetres with a 4.4 cm edge.
Coverage is the figure on the enamel can, typically 350 to 400 sq ft per gallon, and the coverage rates table lists what the main trim and door enamels print. The allowance is 10% for brush and roller work; the hint on the field suggests 35% for spraying, and the spraying guide explains where the rest of the paint goes. Everything from the area onward is the same arithmetic as the paint coverage calculator.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| Door size | 36 × 80 in (90 × 200 cm) | The most common US interior door; 30 and 32 in widths are also standard and the fields accept them |
| Panel factor | 1.15 | Our estimate of the extra surface of raised panels and their mouldings; six-panel doors with deep profiles run closer to 1.2 |
| Glazed factor | 0.6 | Frame, rails and muntins of a typical 10- or 15-lite door, with the glass excluded |
| Louvered factor | 1.6 | Both faces of each slat are painted; the factor is a mid-range figure for standard louvre spacing |
| Door thickness | 1.75 in | Standard for US interior and exterior doors (1.375 in on some interior doors) |
| Coverage | 400 sq ft per gallon | Trim and door enamel data sheets (Benjamin Moore Advance, Sherwin-Williams Emerald Urethane, Behr Urethane Alkyd): 350–400 sq ft per gallon |
| Coats | 2 | Enamel needs two coats for an even sheen; three over a dark colour |
| Allowance | 10% brushed, 35% sprayed | Brush loss on small areas; airless overspray on narrow objects |
Assumptions last reviewed October 7, 2026.
The calculator does not model primer, which bare wood, filled dents and any change from a dark stain to paint need; the primer calculator takes the same area. It does not count the frame or the jamb, which are in the trim calculator, and it assumes the hardware is removed rather than painted around.
Two worked examples
Four panel doors, both sides, brushed
The default: four 36 × 80 in six-panel doors, both faces, two coats at 400 sq ft per gallon, 10% allowance.
- Face: 36 × 80 ÷ 144 = 20 sq ft
- Per door: 20 × 1.15 × 2 sides + 2.4 sq ft of edges = 48.4 sq ft
- All doors: 4 × 48.4 = 194 sq ft
- Per coat: 194 ÷ 400 = 0.484 gallons (1.94 quarts)
- Needed: 0.484 × 2 × 1.10 = 1.06 gallons
- Buy: 1 gallon + 1 quart (1.25 gallons), 0.74 quarts left
The gallon alone would be 6% short. Most people buy the gallon and squeeze; the honest answer is the extra quart, which also does the touch-ups after the hinges go back on.
Twelve doors through a sprayer
A whole house of panel doors taken down and sprayed in the garage, both faces, two coats, allowance set to 35% for overspray.
- All doors: 12 × 48.4 = 581 sq ft
- Per coat: 581 ÷ 400 = 1.451 gallons
- Needed: 1.451 × 2 × 1.35 = 3.92 gallons
- Buy: 4 gallons, 0.32 quarts left
Brushing the same doors would need 3.19 gallons, three-quarters of a gallon less, but a weekend longer. The sprayer usage calculator gives the overspray by setting and surface if you want a figure closer to your own rig.
Where to find your inputs
Number of doors. Count slabs, not doorways: a pair of French doors is two, a bifold closet door with four panels is four narrow slabs (enter their actual width).
Style. Flush means flat; panel means raised or recessed panels with mouldings; French or glazed means mostly glass; louvered means slats. For a door with one large glass pane and a wide frame, use glazed and expect a little extra.
Width and height. Measure the slab, not the opening. Standard interior doors are 80 in tall and 24 to 36 in wide; exterior doors are often 36 × 80 or 36 × 96.
Allowance. 10% for brush and roller, 35% if you are spraying, more if the doors are hung and you are masking around them rather than spraying them flat.
Common mistakes
- Forgetting the edges. Three edges add a tenth of a face; on a dozen doors that is more than a door’s worth of paint.
- Painting one side and wondering why the door warps. Two faces finished differently take up moisture differently. Paint both, or at least seal both.
- Using wall paint. It stays tacky and the door sticks to the stop. Use a trim and door enamel.
- One coat over a dark colour. Three coats, or two over a tinted primer. The coats calculator on this site applies the rule.
- Spraying with a brushing allowance. Overspray on a narrow door is a third of the paint. Set 35%.
- Counting the casings here. They belong to the trim calculator; counting them in both doubles the trim.
Questions people ask
- How much paint does one door take?
- A standard 36 × 80 in panel door is 20 sq ft per face, 23 sq ft with the panel profiles, 46 for both faces plus about 2.4 sq ft of edges. At 400 sq ft per gallon that is about 0.12 gallons per coat, so two coats on one door is under a quart. Four doors come to 1.06 gallons; buy a gallon and a quart.
- Should I paint both sides of a door?
- Usually. Doors between rooms show both faces, and a door painted on one side can bow slightly as the two faces take up moisture differently. Closet and cupboard doors can be done on the outside only, which halves the paint and the calculator allows for it.
- Does a panel door take more paint than a flat one?
- About 15% more, which is the style factor the calculator uses. The raised panels and the mouldings around them add surface, and the brush has to work into the corners. Louvered doors take roughly 60% more and are slow by brush; most are sprayed.
- How much paint do I need to spray doors?
- About a third more than brushing. Airless overspray on a door is high because the door is narrow and much of the fan misses it. Set the allowance to 35% for spraying; with 12 panel doors that is 3.92 gallons instead of 3.19 for brushing.
- Which paint for doors?
- A trim and door enamel, in satin or semi-gloss, because it dries hard, cleans and does not stick to the frame. Wall paint stays soft. Waterborne alkyd enamels level well by brush; conventional latex shows brush marks on large flat panels.
- Are the frames and jambs included?
- No. The door slab only. Casings and jambs are counted in the trim and baseboard calculator at 16 sq ft per doorway, so the two calculators together give the whole doorway.