Paint Calculator

Calculate exactly how many gallons of paint you need for any room. Accounts for walls, ceiling, trim, doors, windows, number of coats, and paint coverage rate.

Room dimensions Walls · Ceiling · Trim
ft
ft
ft
Subtract openings (leave 0 if none)
Each ≈ 21 sq ft
Each ≈ 15 sq ft
Each ≈ 28 sq ft
Paint options
$
Mid-grade paint: $30–$60/gal
Surfaces to paint
Frequently asked questions
How much paint do I need for a 12×12 room? ›
A standard 12×12 room with 9 ft ceilings has about 396 sq ft of wall space. Subtracting a door (21 sq ft) and two windows (30 sq ft) leaves about 345 sq ft to paint. At 350 sq ft/gal coverage with 2 coats, you need about 2.1 gallons — so buy 3 gallons to have a little extra for touch-ups. Add another gallon if you're also painting the ceiling.
How many square feet does a gallon of paint cover? ›
Most paint manufacturers rate their products at 350–400 square feet per gallon per coat on smooth surfaces. On textured, rough, or previously unpainted walls, actual coverage drops to 275–325 sq ft/gal. When in doubt, use the lower end of the coverage range — running short mid-project is far more inconvenient than having a small amount left over for touch-ups.
Do I need primer before painting? ›
Primer is needed when: painting bare drywall, painting over a dark color with a light one, painting over stains or water damage, painting a glossy surface, or transitioning to a very different color. Primer covers at about 250–300 sq ft/gal. Many modern "paint + primer in one" products reduce the need for a separate primer coat, but they don't fully replace dedicated primer on bare surfaces or dramatic color changes.
What paint finish should I use in each room? ›
Flat/matte: bedrooms and ceilings (hides imperfections, not washable). Eggshell: living rooms and dining rooms (slight sheen, moderately washable). Satin: hallways, kids' rooms, playrooms (durable and cleanable). Semi-gloss: kitchens, bathrooms, and trim (moisture resistant, highly washable). High-gloss: doors, cabinets, and trim that need maximum durability and easy cleaning.
Should I roll or spray interior paint? ›
Rolling is better for most DIY interior projects — it uses less paint, creates less overspray mess, and gives a consistent finish on walls and ceilings. Spraying is faster for large projects or when spraying doors, cabinets, or furniture, but requires more prep (masking) and generates more waste. A roller with the right nap thickness (3/8" for smooth walls, 1/2"–3/4" for textured surfaces) is the standard choice for residential interiors.

About this paint calculator

This calculator computes the exact square footage of paintable surface in your room, then divides by your paint's coverage rate and multiplies by the number of coats — giving you the true gallons needed. It separately tracks walls, ceiling, and trim so you can price each color independently.

Always add 10% extra

We automatically add 10% to your total to account for touch-ups, slight waste from rolling, and coverage variation on textured surfaces. Paint doesn't go bad quickly in a sealed can, so having a little extra is always worthwhile for future touch-ups.

Buying paint in the right can size

Buying in gallon cans is almost always more economical than quarts (which are priced at roughly 1.5× the per-gallon rate). If you need 5+ gallons of the same color, a 5-gallon bucket is typically 15–20% cheaper per gallon and ensures perfect color consistency across the entire room.