Paint for a 15×20 room

What a 15×20 room usually is

• Great room
• Open plan living-dining
• Large finished basement
• Games or media room

300 square feet of floor and 560 of wall puts this firmly into two-day territory for one person — not because of the paint, but because prep, cutting in, two coats with proper recoat time between them, and trim will not compress into a single day at an unhurried pace. Rooms this size are also frequently open plan, which raises the question of where the colour stops.

Buy list for a 15×20 room

The paint is rarely the whole bill. For a 15×20 room with a 70 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 15×20 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 15×20 room has a longest wall of 20 ft and a proportion of 1.33:1. 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.

The 1.33:1 proportion means two long walls and two short ones, so budget your time unevenly — the long pair will take noticeably more than half the rolling. It is also worth starting on a long wall while you are fresh and your technique is most consistent.

Worth knowing before you start

In an open plan space, decide where the colour changes before you start, and pick an inside corner or a definite architectural break for it. A colour change that ends in the middle of a flat wall never looks deliberate, no matter how straight the line is.

The arithmetic

Wall area = 2 × (15 + 20) × 8 = 560 sq ft; × 2 coats = 1,120 sq ft; ÷ 350 sq ft per gallon (smooth drywall) = 3.2 → 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 12×12 room
• Paint for a 12×14 room
• Paint for a 12×16 room
• Paint for a 14×14 room
• Paint for a 14×16 room
• Paint for a 16×20 room
• Paint for a 20×20 room

See all room sizes →