Paint Calculator — How Much Paint Do I Need?
Select your project type, enter room dimensions, and instantly get gallons needed, quart options, primer estimate, and a full cost breakdown — for any paint finish.
🎨 Paint Calculator
How to Calculate How Much Paint You Need
The standard formula for interior wall paint is simple: calculate total wall area, subtract doors and windows, divide by coverage rate, then multiply by the number of coats.
Wall area formula: Wall Area = 2 × (Length + Width) × Height
For a 12 × 14 ft room with 8 ft ceilings: 2 × (12 + 14) × 8 = 416 square feet
Subtract openings: Deduct 21 sq ft per door and 15 sq ft per window. One door and two windows = 21 + 30 = 51 sq ft. Paintable area = 416 − 51 = 365 sq ft
Calculate gallons: At eggshell finish (350 sq ft/gal) for 2 coats: 365 × 2 = 730 sq ft total ÷ 350 = 2.09 gallons → round up to 3 gallons
Always round up to the nearest full gallon. Running out mid-wall means a second trip to the store and a risk of color mismatch from a different production batch.
Paint Coverage Guide by Finish Type
Different paint sheens cover different areas per gallon. Higher gloss means more pigment and binder — fewer square feet per coat, but a harder, more washable film.
| Finish | Coverage (sq ft/gal) | Best For | Washability |
|---|---|---|---|
| Flat / Matte | ~400 | Ceilings, low-traffic walls | Low |
| Eggshell | ~350 | Living rooms, bedrooms | Medium |
| Satin | ~350 | Kitchens, hallways, kids' rooms | Good |
| Semi-Gloss | ~300 | Trim, doors, bathrooms | Very Good |
| High-Gloss | ~250 | Cabinets, furniture, accents | Excellent |
How Many Coats of Paint Do You Need?
The number of coats affects your total gallons — and the quality of the finished job:
- 1 coat — Only appropriate for touch-ups or when using the same color over a primed or matching surface. Not recommended for fresh walls or color changes.
- 2 coats — The industry standard for virtually all interior painting projects. Delivers full color saturation, even coverage, and proper hiding. Budget for 2 coats by default.
- 3 coats — Required when making a dramatic color change (dark to light), covering glossy existing paint, or painting over raw drywall without primer. Three-coat jobs use 50% more paint than two-coat jobs.
Do I Need Primer? A Practical Guide
Primer seals the surface, blocks stains, and helps paint bond — but it's not always required.
Always prime when: painting new drywall (drywall primer is mandatory), covering deep stain colors or dark paint, painting over water stains or smoke damage, switching from oil-based to latex paint, or painting over bare wood or metal.
Skip primer when: you're repainting a similar color over a clean, well-adhered existing finish, using a self-priming paint-and-primer in one product, or doing a minor touch-up.
Primer typically costs $18–$30 per gallon and covers about 300 sq ft per coat. One coat of primer is usually sufficient before two coats of finish paint.
Interior Painting Cost Guide
Paint project costs have two components: materials (paint, primer, brushes, tape, drop cloths) and labor (your time or a pro's hourly rate).
| Item | DIY Cost | Pro Cost (labor) |
|---|---|---|
| Budget paint | $25/gal | $2–$3/sq ft labor |
| Mid-range paint | $35–$45/gal | $3–$4/sq ft labor |
| Premium paint | $50–$70/gal | $4–$6/sq ft labor |
| Primer (1 coat) | $18–$30/gal | Included in labor rate |
| Tools (brushes, roller, tape) | $30–$80 one-time | Included in labor rate |
Professional painters typically charge $2–$6 per square foot of paintable wall area, all-in (labor, materials, prep). For a 1,500 sq ft home interior, expect $3,000–$9,000 for a full paint job including ceilings and trim.