Paint Calculator
Free paint calculator. Estimate gallons needed for walls, ceilings, and trim from room dimensions and number of coats — accounts for doors and windows.
Quick answer
Gallons needed = total wall area ÷ 350-400 sqft (one gallon's coverage) × number of coats. Subtract doors and windows from the total. Most interior walls need 2 coats; primer adds another coat if the existing color is much different.
Paint Calculator
How it works
Estimates how many gallons of paint you need based on the room's wall area minus doors and windows. Standard coverage is about 350 sq ft per gallon for one coat on a smooth, primed surface. Most jobs need two coats.
When to use it
Use this before buying paint for a bedroom, living room, hallway, exterior wall, or fence. Also useful when comparing the cost of premium paint (better coverage, fewer coats) vs budget paint (more coats, more labor).
Common mistakes
Underestimating coverage on textured walls or unprimed surfaces — both can cut coverage by 30–50%. Also: forgetting that the first coat on a dark or strong color usually needs primer plus two finish coats, not just two coats of finish.
How the paint calculator works
Wall area = (perimeter of room × wall height). Subtract standard openings — typical interior door is 21 sqft, typical window is 15 sqft. Divide remaining area by paint coverage (350-400 sqft per gallon for most interior latex paints; 200 sqft for textured surfaces or first coats over dramatic color changes). Multiply by number of coats. Round up — partial gallons aren't sold.
When to use it
Estimating paint cost before starting a room makeover. Buying just enough to avoid leftover gallons (paint shelf-life is 2-5 years even unopened). Planning a multi-room project where buying paint in bulk gets a discount. Calculating coverage for textured walls or ceilings that consume more paint than smooth surfaces.
Common mistakes
- Forgetting that ceilings and trim need separate paint. Ceiling paint, wall paint, and trim/door enamel are usually different products. Calculate each separately.
- Painting one coat over a dramatic color change. Going from dark to light, or red to white, requires primer plus 2-3 coats. Cheap paint to save money usually means more coats — premium paint pays for itself.
- Underestimating texture absorption. Stucco, popcorn ceilings, and rough plaster suck up 30-50% more paint than smooth drywall. Adjust coverage downward for textured surfaces.
Frequently asked questions
How much paint do I need for a 12x12 room?
Roughly 1.5 gallons for two coats on a standard 8-foot-tall room with one door and one window. The calculator above accounts for height and openings — enter your specifics for a precise number.
How many coats of paint do I need?
Most rooms need 2 coats for solid coverage. Use 3 coats (or primer + 2) when painting over a dramatic color change, raw drywall, or stained surfaces. Premium paint with self-priming features can sometimes get away with 1 coat over similar-color surfaces.
Does paint coverage differ between brands?
Yes — typically 250-450 sqft per gallon depending on viscosity and hide. The label always lists the manufacturer's claim. Real-world coverage with normal application technique runs 80-90% of the label number.