How Much Paint for a 16x20 Garage? (2026 Guide)
A 16×20 ft garage with 9-ft walls and a 16×7 garage door has about 523 sq ft of net wall — about 3 gallons of topcoat for two coats. Painting the ceiling too adds about 2 gallons.
How many gallons do the walls need?
The floor is 16 × 20 = 320 sq ft, but paint goes on the walls. With 9-ft walls, the perimeter is 2 × (16 + 20) = 72 ft, so the gross wall area is 72 × 9 = 648 sq ft. You don't paint the openings: a common 16×7 double garage door is 112 sq ft (16 × 7), and a side man door plus a window add roughly 13 sq ft more — about 125 sq ft of deductions total. That leaves 648 − 125 = 523 sq ft of net wall.
At roughly 350 sq ft per gallon per coat — the same coverage rate used throughout how many sq ft per gallon of paint — a realistic finish takes two coats: 523 × 2 = 1,046 sq ft, and 1,046 ÷ 350 = 2.99, so you round up to 3 gallons.
| What you're painting | Net area | Topcoat, two coats (rounded up) |
|---|---|---|
| Full-height walls — all 9 ft | 523 sq ft | 3 gallons |
| Wainscot band — bottom 4 ft only | 232 sq ft | 2 gallons |
| Ceiling (optional) | 320 sq ft | 2 gallons |
Order from the full-height row unless you're set on a two-tone finish. A wainscot-only job paints a 4-ft band around the room: 72 × 4 = 288 sq ft of gross, and the opening deductions shrink with it, leaving about 232 sq ft — 232 × 2 = 464 sq ft ÷ 350 = 1.33, which still rounds up to 2 gallons. The optional ceiling is a flat 320 sq ft: 320 × 2 = 640 ÷ 350 = 1.83, so 2 gallons. Walls plus ceiling runs about 5 gallons of topcoat.
Worked example: 16 × 20 with 9-ft walls
Here's the full run of numbers for a typical single-car-plus-storage footprint:
- Perimeter: 2 × (16 + 20) = 72 ft; gross walls 72 × 9 = 648 sq ft.
- Deductions: 16×7 garage door (112 sq ft) + side door and window (≈ 13 sq ft) ≈ 125 sq ft → 648 − 125 = 523 sq ft of net wall.
- Two coats: 523 × 2 = 1,046 sq ft. At 350 sq ft per gallon, 1,046 ÷ 350 ≈ 2.99 → 3 gallons of topcoat. Add 2 gallons if the ceiling gets painted.
Shopping and prep tips
- Deduct the full garage door opening — measure the door leaf itself (16 × 7 = 112 sq ft), not just the frame you see.
- Prime bare drywall first. One coat of drywall primer or primer-sealer before the color seals the joints and evens absorption; it's bought separately from the 3 gallons of topcoat.
- Garage floors aren't paint. A concrete slab gets floor-rated epoxy or concrete floor paint, so it isn't part of this wall estimate — keep the 320 sq ft of floor out of the paint-gallon count.
- Watch texture and porosity. Smooth drywall hits 350 sq ft per gallon; heavy texture or raw masonry can cut coverage by 25% or more, so bump the order up.
When the numbers change
A 16×20 is a compact garage, and many owners use it for one car plus storage. If yours is a true two-car footprint, the walls are taller and the openings bigger — see how much paint a 2-car garage needs for that model. If the next job is below grade rather than at grade, how much paint a basement needs follows different wall rules.
FAQ
How many gallons of paint do the walls of a 16x20 garage need?
About 3 gallons of topcoat for two coats. The walls total roughly 523 sq ft of net area: a 72-ft perimeter × 9-ft walls = 648 sq ft, minus about 125 sq ft of doors and windows. Two coats double it to 1,046 sq ft, and at 350 sq ft per gallon that's 2.99 — rounded up to 3 gallons.
Do I subtract the garage door area when I measure the walls?
Yes — deduct the whole opening. A typical 16×7 double garage door is 112 sq ft (16 × 7), and a side man door plus a window add roughly 13 sq ft more, for about 125 sq ft of deductions total — that's what takes the 648 sq ft of gross wall down to 523 sq ft.
Should I paint a 16x20 garage ceiling?
It's optional. The 3-gallon figure covers the walls only. If you paint the ceiling too, add about 2 gallons: the 16×20 ceiling is 320 sq ft, 320 × 2 coats = 640 sq ft ÷ 350 sq ft per gallon ≈ 1.8, rounded up to 2 gallons.
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