How to use this calculator
Measure your room's length and width in feet, then enter the ceiling height (most standard rooms are 8 feet). Add the number of doors and windows so the calculator can subtract those areas — you don't need to paint over them.
Choose 1 or 2 coats. Two coats are recommended for most projects, especially when changing colors. The calculator will show exactly how many gallons (or quarts, for smaller areas) you need, plus an estimated cost range based on typical interior paint prices.
This calculator assumes standard door sizes (3' × 7' = 21 sq ft) and standard window sizes (3' × 5' = 15 sq ft). If your doors or windows are significantly larger, you may need slightly less paint.
Paint finish guide
Choosing the right paint finish matters as much as choosing the right color. Higher-sheen finishes are more durable and washable but show wall imperfections more. Lower-sheen finishes hide flaws but are harder to clean.
| Finish | Sheen level | Best for |
|---|---|---|
| Flat/Matte | 0-5% | Ceilings, adult bedrooms, formal dining rooms |
| Eggshell | 10-25% | Living rooms, bedrooms, dining rooms |
| Satin | 25-35% | Family rooms, hallways, kids' rooms, laundry |
| Semi-Gloss | 35-70% | Kitchens, bathrooms, trim, doors, cabinets |
| Gloss | 70-90% | Front doors, furniture, accent pieces |
How much paint do I really need?
The standard rule is that one gallon of paint covers about 350 square feet of smooth, primed wall surface. But real-world coverage depends on several factors: wall texture, paint color, surface porosity, and application method.
Rough or textured walls (like knockdown or orange peel texture) absorb more paint and can reduce coverage to 250-300 square feet per gallon. Painting over a dark color with a light one often requires an extra coat or a tinted primer to avoid the old color bleeding through.
When in doubt, buy an extra gallon. Unopened paint can be returned to most stores, and having leftover paint for future touch-ups is always better than running out mid-wall — which can leave visible lap marks where wet paint meets dried paint.
Frequently asked questions
How much paint do I need for a 12×12 room?
A 12×12 room with 8-foot ceilings has about 384 sq ft of wall space. After subtracting a door (21 sq ft) and two windows (30 sq ft), you have roughly 333 sq ft of paintable area. For two coats, you need about 1.9 gallons — so buy 2 gallons.
How many square feet does a gallon of paint cover?
One gallon of interior paint typically covers about 350-400 square feet per coat on smooth, primed surfaces. Rough or textured walls, unpainted drywall, and porous surfaces will reduce coverage to around 250-300 square feet per gallon.
Do I need one coat or two coats of paint?
Two coats are recommended for most painting projects. One coat may be sufficient when painting the same or very similar color over a well-primed surface. Two coats ensure even coverage, true color, and better durability.
What paint finish should I use for a bathroom?
Semi-gloss is the best finish for bathrooms. It resists moisture and humidity, is easy to clean, and holds up well in high-moisture environments. Satin is also acceptable for bathrooms with good ventilation.