Paint Calculator - Estimate Paint Gallons Needed for Any Room

How to Use the Paint Calculator

1. Enter room dimensions — input the room’s length, width, and height in feet
2. Subtract openings — enter the number of windows and doors (standard sizes are subtracted automatically)
3. Choose coats — select 1 or 2 coats (2 coats recommended for most paint jobs)
4. Include ceiling — toggle whether you are painting the ceiling
5. Get gallons — instant estimate for walls, ceiling, and trim, rounded up to the nearest gallon

Perfect for homeowners, painters, and contractors planning interior painting projects. All calculations are done in your browser — no data is sent anywhere.

Features

• Walls, ceiling, and trim — separate estimates for each surface type
• Door/window subtraction — automatically subtracts 20 sq ft per door and 15 sq ft per window
• Multiple coats — doubles the paint needed when selecting 2 coats for proper coverage
• Gallon precision — rounds up to the nearest gallon so you never run short
• Waste allowance — includes a 10% buffer for spillage, touch-ups, and uneven surfaces
• Standard paint coverage — uses 350 sq ft per gallon (industry standard for most paints)

Use Cases

Homeowners planning a DIY paint project can estimate how many gallons to buy before heading to the store. Instead of guessing or measuring wrong, they get an accurate count that prevents both overbuying and running out mid-project.

Painting contractors use the calculator to prepare quotes and estimates for clients. A quick room measurement gives them the material cost breakdown they need for accurate bids.

Property managers painting multiple units calculate paint requirements for standard room sizes and bulk-order the right quantity, saving trips to the hardware store.

Interior designers include paint quantities in their project specifications. The calculator helps them determine whether a single gallon is enough for an accent wall or if multiple gallons are needed for a full room.

FAQ

How much area does a gallon of paint cover?

One gallon of paint typically covers approximately 350-400 square feet of smooth surface. This calculator uses 350 sq ft per gallon for a conservative estimate.

Should I always buy 2 coats worth of paint?

For most interior paint jobs, two coats provide better coverage, color depth, and durability. One coat may suffice if you are painting over a similar color with high-quality paint, but two coats give professional results.

Do I need to subtract windows and doors manually?

No. The calculator automatically subtracts 20 sq ft for each standard door and 15 sq ft for each standard window from the wall area.

What about trim and baseboards?

Trim paint is estimated separately based on the room perimeter. A separate trim paint calculation helps you buy the right product — trim usually requires a different paint finish (semi-gloss or gloss) than walls.

How do I measure a room for painting?

Measure the length and width of the floor, then the height from floor to ceiling. Multiply the perimeter by the height to get total wall area. Measure window and door openings separately for subtraction.

Tips

• Always buy a little extra paint — the 10% buffer built into the calculator accounts for texture, spillage, and touch-ups
• Use the same brand and finish for all walls in a room to ensure color consistency
• For textured walls (popcorn, orange peel), increase your estimate by 15-20% — texture absorbs more paint