Paint Your Space Without the Guesswork
Buying the right amount of paint saves you a wasted trip to the store and hundreds of dollars in leftover cans. Enter your room dimensions, ceiling height, doors, and windows, and this calculator tells you exactly how many gallons of paint you need - for one coat or two. Works for interior and exterior walls, ceilings, and trim. Runs entirely in your browser.
How Much Paint Do You Actually Need?
Paint coverage is measured in square feet per gallon. Most interior wall paints cover 350 to 400 square feet per gallon on smooth, previously-painted surfaces. Premium paints tend to cover more; economy paints often cover less.
The calculation for a single room is:
- Measure the total wall area: (Length + Width) x 2 x Wall Height
- Subtract doors (about 20 sq ft each) and windows (about 15 sq ft each)
- Divide by the paint's coverage per gallon (usually 350)
- Multiply by the number of coats (typically 2)
- Round up to the nearest gallon
Our calculator does all five steps instantly.
Paint Coverage Per Gallon (Common Types)
| Paint Type | Coverage (sq ft/gal) | Best For |
|---|---|---|
| Flat / Matte | 350 | Low-traffic ceilings, low-sheen walls |
| Eggshell | 400 | Living rooms, bedrooms |
| Satin | 400 | Kitchens, bathrooms, hallways |
| Semi-Gloss | 350 | Trim, doors, cabinets |
| Primer | 250 | Bare drywall, stains, color changes |
| Exterior paint | 300 | Rough siding, stucco, brick |
How to Use This Paint Calculator
- Choose what you are painting: walls, ceiling, trim, or exterior.
- Enter the room's length and width in feet.
- Enter the wall height (8 ft is standard; 9-12 ft for taller rooms).
- Add the number of doors and windows to subtract their area.
- Pick the number of coats (we recommend 2 for a uniform finish).
- Click Calculate - the result is in gallons, rounded up to the nearest whole gallon.
Worked Example: 12 x 12 Bedroom
Room dimensions: 12 ft x 12 ft, 8 ft ceiling, one door, two windows.
- Wall area: (12 + 12) x 2 x 8 = 384 sq ft
- Subtract door: 384 - 20 = 364 sq ft
- Subtract 2 windows: 364 - 30 = 334 sq ft
- Two coats: 334 x 2 = 668 sq ft
- Divide by 350 coverage: 668 / 350 = 1.91 gallons
- Round up: 2 gallons of wall paint
Add 1 gallon of ceiling paint and 1 quart of trim paint for a complete room refresh.
Paint Amount by Room Size
| Room Size | Wall Paint (2 coats) | Ceiling | Trim |
|---|---|---|---|
| 10 x 10 bedroom | 1.5 gal | 1 gal | 1 qt |
| 10 x 12 bedroom | 2 gal | 1 gal | 1 qt |
| 12 x 16 master | 2.5 gal | 1 gal | 1 qt |
| 15 x 20 living | 3 gal | 1.5 gal | 2 qt |
| 5 x 8 bathroom | 1 gal | 0.5 gal | 1 qt |
Do You Really Need Two Coats?
Yes - in almost every case. Two coats:
- Hide roller marks and brush strokes
- Ensure uniform color across the wall
- Create a more durable finish that washes better
- Reduce visible wall imperfections
Exceptions: repainting the exact same color in good condition, or using a premium one-coat paint. Even then, a second coat usually pays off in appearance.
When to Use Primer
Primer is required in these situations:
- Painting bare drywall or new wood
- Switching from a dark color to a light one
- Covering stains, water marks, or smoke damage
- Painting over glossy surfaces
- Painting over repairs or patched areas
Budget 1 extra gallon of primer for a standard bedroom, or 0.5 gallon for a bathroom.
How to Save Paint (Without Cutting Corners)
- Use a quality brush and roller - cheap tools waste paint
- Tint your primer toward the topcoat color to reduce coats needed
- Wrap brushes and rollers in plastic between coats - no washing = no waste
- Use the right finish for the job (eggshell for walls, satin for trim)
- Store leftover paint labeled with the room and date for future touch-ups
Paint Cost Estimate (2026 US Averages)
- Interior wall paint: $25-$60 per gallon
- Ceiling paint: $15-$30 per gallon
- Trim paint (semi-gloss): $20-$40 per quart
- Primer: $15-$30 per gallon
- Rollers, brushes, tape, drop cloths: $25-$50 per room
Total DIY cost for one bedroom: $100-$200 in materials.
Frequently Asked Questions
How much paint do I need for a 10x10 room?
About 1.5 gallons for walls at two coats, plus 1 gallon for the ceiling and 1 quart for trim. Round up to 2 gallons for walls to be safe.
Will one gallon of paint cover a bedroom?
Only for a single coat in a small bedroom (10x10 or smaller). For two coats - the standard - you need about 2 gallons.
How many square feet does a gallon of paint cover?
350 to 400 sq ft on smooth, previously-painted walls, depending on paint quality. Rough or textured surfaces reduce coverage by 20-30%.
Do I need primer before painting?
Yes if you are painting bare drywall, covering a dark color with a light one, or painting over stains or glossy surfaces. Otherwise, a quality self-priming paint can work.
How long does paint take to dry between coats?
Latex and acrylic paints are typically dry to the touch in 1 hour, recoatable in 2-4 hours, and fully cured in 24-72 hours depending on humidity.
Can I use ceiling paint on walls?
Technically yes, but ceiling paint is flat and less durable. For walls, use an eggshell or satin finish.
How much does it cost to hire a painter?
Professional interior painting costs $2-$6 per square foot of wall area, or roughly $300-$800 for a single room in most US markets.
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