Paint Calculator
Calculate exactly how many gallons of paint you need for any room. Accounts for doors, windows, number of coats, and optional ceiling — so you buy the right amount on the first trip.
Planning a bigger outdoor project? Try the Deck Calculator →
This paint calculator eliminates the guesswork of estimating how much paint you need for any room. Instead of eyeballing gallons at the hardware store, enter your room's length, width, and wall height, then subtract out the doors and windows that won't get painted. The calculator handles two coats automatically, adds ceiling coverage if you select it, and gives you a precise gallon count — so you stop wasting money on extra cans and stop making second trips back to the store when you run short mid-wall.
How to Use the Paint Calculator
- Enter your room's length and width in feet.
- Enter the wall height — 8 feet is standard for most rooms.
- Enter the number of doors and windows; the calculator subtracts 20 sq ft per door and 15 sq ft per window.
- Choose the number of coats — two coats are recommended for full coverage and durability.
- Select "Walls + Ceiling" if you're painting the ceiling too.
- Adjust the coverage rate if your paint label specifies a different number — 350 sq ft per gallon is the standard planning estimate.
- Click "Calculate Paint" to see your wall area, wall gallons, ceiling gallons, and total gallons needed.
Paint Calculation Example: 12×14 Room
A standard 12-foot by 14-foot bedroom with 8-foot walls, 2 doors, 2 windows, and 2 coats of paint:
| Step | Value |
|---|---|
| Wall area (2 × (12 + 14) × 8) | 416 sq ft |
| Door deduction (2 × 20) | 40 sq ft |
| Window deduction (2 × 15) | 30 sq ft |
| Net paintable area | 346 sq ft |
| × 2 coats | 692 sq ft to cover |
| At 350 sq ft per gallon | 2 gallons needed |
In this example the 346 sq ft net area × 2 coats = 692 sq ft total, and 692 ÷ 350 = 1.98, which rounds up to 2 gallons. Running out after one coat and needing a third store trip — or worse, opening a second batch that doesn't match — costs far more than buying right the first time.
Frequently Asked Questions
How many gallons of paint do I need for a 12x12 room?
A 12×12 room with 8-foot ceilings has 384 sq ft of wall area. Subtracting 2 doors (40 sq ft) and 2 windows (30 sq ft) leaves 314 sq ft. At 350 sq ft per gallon with 2 coats, you need about 2 gallons. Always round up — running out mid-wall means a second store run and potential sheen mismatch from different batches.
How much does one gallon of paint cover?
Standard interior paint covers 350–400 sq ft per gallon on smooth, primed surfaces. Textured walls, dark colors, and new drywall absorb more paint and may only yield 250–300 sq ft per gallon. Use 350 as a safe planning number; adjust down for rough surfaces or color-saturated paints.
Do I need two coats of paint?
Almost always yes. A single coat rarely achieves full opacity, especially when covering a different color or painting new drywall. Two coats produce a more even finish, true color, and better durability. The only exception is paint-and-primer combos on neutral re-paints — even then, two coats are usually worth it.
How do I calculate paint for a ceiling?
Ceiling area = length × width. A 12×14 room has a 168 sq ft ceiling. At 350 sq ft per gallon with one coat, that's about half a gallon — buy a quart. Ceilings typically only need one coat since they rarely need a full color change. This calculator adds ceiling gallons separately so you can plan both in one step.
What is the difference between a gallon and a quart of paint — when should I buy each?
A quart covers about 87–100 sq ft — one coat in a small bathroom or a single accent wall. A gallon covers 350–400 sq ft — one coat in a standard bedroom. For whole-room jobs, buy gallons; they're cheaper per square foot. Buy a quart only for ceilings, touch-ups, or rooms under 150 sq ft.