Buy too little paint and you're back at the store mid-wall, hoping the new batch matches. Buy too much and you've wasted $60 a gallon. The math takes two minutes.
THE FORMULA
- Measure the perimeter: add the length of every wall.
- Multiply by ceiling height to get wall area.
- Subtract openings: about 20 sq ft per door and 15 sq ft per window.
- Divide by 350, the typical coverage per gallon per coat.
- Multiply by 2 for two coats.
Example: a 12×12 bedroom with 8-foot ceilings has 48 × 8 = 384 sq ft of wall. Minus one door and two windows (50 sq ft) leaves 334 sq ft. Two coats = 668 sq ft ÷ 350 ≈ 2 gallons.
QUICK CHART
| Room (8 ft ceilings) | Walls, 2 Coats | Ceiling, 2 Coats |
|---|---|---|
| Bathroom (5×8) | 1 gallon | 1 quart |
| Small bedroom (10×10) | 1.5 – 2 gallons | 1 gallon |
| Bedroom (12×12) | 2 gallons | 1 gallon |
| Primary bedroom (14×16) | 2.5 – 3 gallons | 1.5 gallons |
| Living room (16×20) | 3 – 3.5 gallons | 2 gallons |
Trim: a typical room's baseboards, door casing and window casing take about 1 quart for two coats. A door takes about 1 quart for both sides.
WHEN YOU'LL NEED MORE
- Big color change: going from dark to light, or to deep reds and yellows, may need a primer coat or a third coat.
- New drywall or patches: unprimed drywall soaks up paint; prime first.
- Textured walls: more surface area; add 10–20%.
- Higher ceilings and stairwells: measure the actual height.
BUYING TIPS
- When you need 3 or more gallons, buy a 5-gallon bucket; it's usually cheaper and the color is consistent.
- If you buy separate gallons, mix them together in a bucket (called “boxing”) so color is uniform.
- Keep a labeled quart for touch-ups.
Paint is usually 15–20% of a professional painting price; the rest is prep and labor. For full project numbers, see interior painting costs.
RELATED READING
INTERIOR PAINTING COST IN DC, MD & VA (2026 GUIDE)
Everything you need to know about painting costs in the DMV area, from single rooms to whole-house projects.
HOW TO CHOOSE THE RIGHT PAINT FINISH FOR EVERY ROOM
Flat, eggshell, satin, semi-gloss — which finish belongs where and why the wrong choice causes real problems in certain rooms.
DIY VS. PROFESSIONAL PAINTING: WHEN TO CALL THE PROS
Honest breakdown of when it makes sense to grab a roller yourself and when hiring a professional actually saves you money.
Planning a project? See our Interior Painting service page for scope, process and recent work.
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