Understanding your result
The headline is the paint for the number of doors and coats you chose, with the allowance, and the sub-line is the can list. The three figures show the area, the paint per coat and the cans.
The breakdown shows the door face from its width and height, the style factor, the sides, the frame and jamb trim per door if you ticked it, and the total area for all the doors, followed by the coverage, coats, allowance, total and can lines. For a single door the quantity is under a gallon, and the choice is between three quarts and a gallon; the gallon is nearly always the better buy, as the result shows with the leftover.
The garage door is part of a larger exterior job more often than not. The exterior house paint calculator does the siding and counts the garage opening as three or six doors; the exterior trim calculator does the fascia, soffits and the other casings, but not this doorway’s frame, which is included here. For interior doors the door paint calculator uses the same style factors on a smaller panel.
How we calculate this
The standard sizes are the common US ones: 8 × 7 ft for a single door (56 sq ft) and 16 × 7 ft for a double (112 sq ft); 9 × 7, 9 × 8 and 18 × 8 are also sold, and the custom option takes any size. The style factor is the same idea as on the interior door calculator: raised or recessed panels add about 15% for their profiles and edges, carriage-style doors with applied trim boards about 25%, flat and ribbed doors nothing. The frame and jamb trim is the 6 in wide band around the opening (jamb and stop), about 15 sq ft on a double door, which is painted with the door because it is the same colour. The standard sizes page lists the door sizes with the other openings.
Coverage is the exterior paint’s figure, 350 to 400 sq ft per gallon on a smooth steel or primed wood surface; the coverage rates table has the published figures. The allowance is 10% for brush and roller; the field hint suggests 35% for spraying, and the spraying guide explains where the rest goes on a door with the driveway behind it.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| Single door | 8 × 7 ft | The most common US single garage door size |
| Double door | 16 × 7 ft | The most common US double size |
| Panel factor | 1.15 | Raised and recessed panels, as on the interior door calculator; site estimate |
| Carriage factor | 1.25 | Applied trim boards and their edges; site estimate |
| Frame trim | 0.5 ft wide band around the opening | A 6 in jamb and stop; site estimate |
| Coverage | 350 sq ft per gallon | Exterior acrylic data sheets (Sherwin-Williams, Benjamin Moore, Behr): 350–400 on smooth surfaces |
| Coats | 2 | Manufacturers’ recommendation for a colour change |
| Allowance | 10% brushed, 35% sprayed | Brush and roller loss; airless overspray on a door with open space behind it |
Assumptions last reviewed October 7, 2026.
The calculator does not model primer, which bare wood, rust spots and a glossy factory finish need (spot-prime rust with a metal primer; the primer calculator gives a quantity for a wood door), windows in the top panel, which reduce the area by a square foot or two each, or the weather seals, which are masked. The exterior measuring guide has the garage door among the openings to count when measuring the siding.
Two worked examples
One double raised-panel door with its frame
16 × 7 ft, outside only, frame trim included, two coats at 350 sq ft per gallon, brushed and rolled.
- Face: 16 × 7 = 112 sq ft; per door: 112 × 1.15 × 1 = 129 sq ft
- Trim: (2 × 7 + 16) × 0.5 = 15 sq ft
- Area: 144 sq ft
- Per coat: 144 ÷ 350 = 0.411 gallons (1.64 quarts)
- Needed: 0.411 × 2 × 1.10 = 0.904 gallons, or 3.62 quarts, buy 1 gallon
A gallon with a third of a quart over. Two single flat doors painted on both sides with one coat and no trim, for comparison, are 224 sq ft and 2.56 quarts: three quarts.
A custom 18 × 8 carriage door, sprayed
One door, outside only, carriage style with applied trim, frame included, two coats, allowance set to 35% for the sprayer.
- Face: 18 × 8 = 144 sq ft; per door: 144 × 1.25 = 180 sq ft
- Trim: (2 × 8 + 18) × 0.5 = 17 sq ft; area 197 sq ft
- Per coat: 197 ÷ 350 = 0.563 gallons
- Needed: 0.563 × 2 × 1.35 = 1.52 gallons, buy 1 gallon + 3 quarts
Two gallons, in practice. Brushed, the same door would need 1.24 gallons: the sprayer costs most of a quart in overspray and saves an afternoon.
Where to find your inputs
Size. Single or double covers most doors; measure the slab for anything else, width across and height from the floor to the top of the top panel.
Style. Flat or ribbed (short horizontal grooves), raised or recessed panels (rectangles pressed into the steel), or carriage style (applied boards, cross-bucks, decorative hinges).
Sides. Outside only unless the inside is being painted too.
Frame trim. Tick it if the jamb and stop around the opening are the same colour and being painted with the door; untick if they are part of the trim job in the exterior trim calculator.
Common mistakes
- Painting the seals and tracks. They stick and tear. Mask them.
- Oil-based paint on a steel door. It cracks as the steel expands. Use 100% acrylic.
- Skipping the wash. Road film and chalk under the paint is the usual cause of peeling.
- Rolling raised panels with a wide roller. The edges are missed; a brush does the panel edges first.
- Painting with the door open in the sun. The panels get hot and the paint flashes; paint it closed, in shade or early.
- Counting this doorway in the trim calculator too. The frame is here, once.
Questions people ask
- How much paint does a double garage door take?
- A 16 × 7 ft raised-panel door is 112 sq ft of face, about 129 with the panels, plus 15 sq ft of frame trim around the opening, so 144 sq ft. Two coats at 350 sq ft per gallon with a 10% allowance is 0.9 gallons, so one gallon with a little left for touch-ups.
- Do I paint the inside of the door?
- Usually not. The inside of a steel door has the factory finish and is rarely seen; the outside is what weathers. If the inside is to be painted too, tick both sides and the quantity doubles.
- Which paint for a steel garage door?
- A 100% acrylic exterior paint, satin or semi-gloss, over a clean, scuffed surface with any rust spot-primed with a metal primer. Oil-based paints chalk and crack on steel that expands in the sun. Wood doors take the same exterior paint over a primer.
- How much more paint does a carriage-style door take?
- About 25% more than a flat door, which is the factor the calculator uses, for the applied trim boards and their edges. A raised or recessed panel door takes about 15% more; a flat or ribbed door takes the face area as it is.
- Should I spray a garage door?
- It gives the smoothest finish on a flat door and is the quick way to do two or more, but the overspray lands on the driveway, the siding and the car. Mask well and set the allowance to 35%. A 4 in foam roller and a brush for the panel edges is the usual compromise.
- What about the weather seals and the tracks?
- Do not paint them. The bottom seal, the side seals and the rollers and tracks should be masked or kept clear; paint on a seal makes it stick and tear. Paint the door with it closed for the outside, open in sections for the inside.