Paint for a 20×20 room

What a 20×20 room usually is

• Open plan great room
• Large finished basement
• Studio or workshop
• Converted garage

400 square feet of floor, 640 of wall — the largest room on this site and a weekend project rather than a day one. Two coats needs the best part of a 5 gallon pail, and the cutting-in alone runs to 160 linear feet per coat. If two of you can work it, one cutting in ahead while the other rolls behind, the job roughly halves; done alone it is a genuine two days.

Buy list for a 20×20 room

The paint is rarely the whole bill. For a 20×20 room with a 80 ft perimeter:

Primer is listed as conditional because it genuinely is. Previously painted walls in good condition, going a similar colour, do not need it. Bare drywall, patched repairs, water stains, or a dramatic colour change all do — and skipping it there costs you an extra finish coat, which is more expensive than the primer was.

This is a two-day paint job

That is hands-on time for one person at an unhurried pace, and it excludes drying. Add two to four hours between coats — the recoat time on the can, not the touch-dry time — so a job this size realistically spans two days. A second person cutting in while the first rolls does not halve the total, but it comes close.

What still changes the gallon count

Four things move the gallon count on a 20×20 room, and they are worth knowing before you buy rather than after:

Notice which of those actually changes the number. Surface texture usually does — a bare or heavily textured wall drops coverage from 350 to about 250 sq ft per gallon, which is enough to add a full gallon. Deducting openings usually does not: a door and two windows come to about 50 sq ft, and after rounding up to whole gallons the saving generally vanishes. That is why this site leaves openings in by default — the small surplus becomes your cut-in buffer and your touch-up paint. Sheen does not change this table — see which paint sheen.

The long walls are the job

A 20×20 room has a longest wall of 20 ft and a proportion of 1:1. That matters more than it sounds, because wall area alone does not tell you how the job will go — a 12×16 and a 14×14 room have exactly the same 448 sq ft of wall and the same perimeter, but they paint quite differently.

At 20 ft, the long walls here are past the point where you can comfortably keep a wet edge across the whole run. Lap marks are the risk on this room — the visible stripe you get when fresh paint meets paint that has already started to set. Work in vertical sections roughly a roller-width-and-a-half wide, always rolling back into the wet edge of the last section, and finish the whole wall before you stop. A break halfway along a 20 ft wall shows.

Being close to square, the four walls are near-identical, which makes this an easy room to plan: whatever rhythm you settle into on the first wall carries through the other three. It also means a single 9 × 12 ft drop cloth run along each wall covers the working area comfortably.

Worth knowing before you start

Order the work so nothing dries while you wait: cut in one wall, roll it, move on. Cutting in the entire room first means the earliest edges are fully dry before the roller reaches them, and dry cut-in lines show through as a visible frame around each wall — the effect painters call picture framing.

The arithmetic

Wall area = 2 × (20 + 20) × 8 = 640 sq ft; × 2 coats = 1,280 sq ft; ÷ 350 sq ft per gallon (smooth drywall) = 3.66 → round up to 4gallons. Trim and time come from standard rates — 250 sq ft/hour rolling and 60 linear ft/hour cutting in — all documented in how we calculate. The full reasoning is in how much paint do I need?, and if you are weighing it against a quote, see what it costs to paint a room.

Other room sizes

• Paint for a 12×16 room
• Paint for a 14×14 room
• Paint for a 14×16 room
• Paint for a 15×20 room
• Paint for a 16×20 room

See all room sizes →