Paint Calculator — Estimate Gallons & Coverage for Any Room
Enter your room's length, width, and ceiling height along with the number of doors and windows. The calculator deducts standard opening areas, multiplies by your chosen coat count, and divides by the paint's coverage rate to give you the exact gallons and quarts needed — no guesswork.
Paint Calculator
Estimate gallons and quarts needed to paint any room
Room Dimensions (feet)
Openings (subtracted from wall area)
21 sq ft each
15 sq ft each
Number of Coats
Standard latex paint: 350 sq ft/gal. Premium or thick paint: 250–300 sq ft/gal.
Frequently Asked Questions
How do I calculate how much paint I need for a room?
Multiply the room perimeter (2 × length + 2 × width) by the ceiling height to get total wall area in square feet. Subtract 21 sq ft per door and 15 sq ft per window. Multiply by the number of coats planned, then divide by the paint's coverage rate (typically 350 sq ft per gallon). Round up to the nearest gallon.
How many gallons of paint do I need for a 12x10 room with 8-foot ceilings?
A 12×10 room with 8-foot ceilings has a wall area of 352 sq ft. With one standard door (21 sq ft) and two windows (30 sq ft), the paintable area is 301 sq ft. For 2 coats at 350 sq ft/gal, you need 2 gallons of paint.
How much does one gallon of paint cover?
One gallon of standard latex paint typically covers 350–400 sq ft per coat on smooth, primed drywall. Rough or porous surfaces (brick, unprimed drywall, textured walls) reduce coverage to 200–300 sq ft. Premium thick paints may cover 250–300 sq ft. Always check the label for the manufacturer's stated coverage.
How many coats of paint do I need?
Two coats is the standard recommendation for most paint jobs. Use one coat for refreshing the same color over good existing paint. Use three coats when covering very dark or saturated colors (deep red, navy, black), going from dark to light, or painting over stains and bare drywall without primer.
Should I buy paint by the gallon or quart?
Gallons are more economical for large areas — a gallon costs roughly 25–35% less per quart than buying quarts individually. Buy quarts for small accent walls, touch-ups, or areas under 100 sq ft. For most rooms needing 2+ gallons, buying gallon cans is the better value.
Do I need to paint the ceiling separately?
Yes — this calculator covers walls only. Ceiling paint is a separate calculation: multiply room length by width to get ceiling area, then divide by coverage (300–400 sq ft/gal for flat ceiling paint). Ceilings typically only need one coat unless covering significant stains.
What is the standard door and window area used in paint calculations?
A standard interior door is approximately 3 feet wide × 7 feet tall = 21 sq ft. A standard double-hung window is approximately 3 feet wide × 5 feet tall = 15 sq ft. For oversized doors, sliding glass doors, or large picture windows, increase the count or add extra sq ft manually.
How much extra paint should I buy for touch-ups?
Buy at least one extra quart beyond your calculated amount for touch-ups, mistakes, and future repairs. For walls where you want an exact color match later, keeping a sealed quart in storage is ideal — paint batches can vary slightly between purchases, and stored paint lasts 2–10 years if kept sealed and away from freezing temperatures.
Paint Calculator: Coverage, Coats & Gallons Guide
This paint calculator estimates how many gallons and quarts of paint are needed to cover the walls of a room. It deducts standard door and window areas from the total wall surface, then divides by your paint's coverage rate and the number of coats planned.
Paint Coverage Formula
Step 1 — Wall Area
The perimeter of the room multiplied by the ceiling height gives total wall area in square feet.
Step 2 — Deduct Openings
Standard door = 21 sq ft (3′ × 7′). Standard window = 15 sq ft (3′ × 5′).
Step 3 — Gallons
Result is rounded up to the nearest whole gallon.
Coverage by Paint Type
Coverage varies by sheen, brand, and substrate. Use these as starting estimates and check the label for the exact coverage rate.
| Paint Type / Sheen | Coverage (sq ft/gal) | Best For | Notes |
|---|---|---|---|
| Flat / Matte | 350–400 | Ceilings, low-traffic walls | Hides imperfections; hard to clean |
| Eggshell | 300–350 | Living rooms, bedrooms | Slight sheen; wipeable |
| Satin | 300–350 | Hallways, kids' rooms | Durable; shows brush marks |
| Semi-Gloss | 250–300 | Kitchens, bathrooms, trim | Washable; reflects light |
| Gloss / High-Gloss | 200–250 | Doors, cabinets, trim | Maximum durability; shows flaws |
Room Measuring Tips
- Measure each wall's length at the floor level and use the highest ceiling measurement for height.
- Round up fractional feet to the nearest half-foot for a safety buffer.
- For L-shaped or irregularly shaped rooms, break them into rectangles and add the wall areas.
- A standard interior door is 32–36 inches wide × 80 inches tall (≈ 21 sq ft).
- A standard double-hung window is 36 inches wide × 60 inches tall (≈ 15 sq ft).
- For large picture windows or sliding glass doors, increase the window count accordingly.
How Many Coats Do You Need?
1 coat
Refresh of same color, or when painting over a fresh primer that closely matches the finish color. Not recommended for color changes or new drywall.
2 coats (recommended)
Standard for most projects. Provides even, opaque coverage for color changes, medium-tone-to-light changes, and high-quality finishes.
3 coats
Needed when painting over very dark or saturated colors (deep red, navy, black), covering stains, or using a very light color over a dark substrate.
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