Paint Calculator

Calculate exactly how much paint you need for your next project. Enter your room's length, width, and ceiling height, then specify the number of doors and windows to subtract from the paintable area. The Paint Calculator returns the gallons of paint required based on standard coverage rates, accounting for two coats — so you buy just the right amount without waste or extra trips to the store.

ft
ft
ft

Each standard door is approx. 21 sq ft (3×7 ft)

Each standard window is approx. 15 sq ft (3×5 ft)

sq ft/gal

Check your paint can label — typically 350–400 sq ft per gallon

Results

Gallons of Paint Needed

--

Total Paintable Area

--

Recommended Gallons to Buy

--

Or Buy in Quarts

--

Wall Area

--

Ceiling Area

--

Area Deducted (Doors & Windows)

--

Paintable Surface Breakdown

Frequently Asked Questions

How much area does a gallon of paint cover?

A standard gallon of paint typically covers 350 to 400 square feet per coat on smooth surfaces. Textured or porous walls may require more paint. Always check the coverage rate on your specific paint can label for the most accurate estimate.

Should I calculate for one coat or two coats of paint?

Most painting projects require two coats for full, even coverage — especially when switching colors or covering dark shades. One coat may be sufficient for touch-ups or when using a paint-and-primer-in-one product. This calculator lets you select your desired number of coats.

Do I need to subtract door and window areas?

Yes, it's good practice to subtract the area of doors and windows since they won't be painted. A standard door is roughly 21 square feet (3 ft × 7 ft) and a standard window is about 15 square feet (3 ft × 5 ft). This calculator deducts these automatically based on the counts you enter.

Should I include the ceiling in my paint estimate?

That depends on your project. Ceilings are often painted a different color (usually white) and require a separate paint type. Use the 'Include Ceiling' option in the calculator to add ceiling area to your estimate if you're painting it the same color as your walls.

How do I convert square feet to gallons of paint?

Divide your total paintable area (in square feet) by the coverage rate per gallon, then multiply by the number of coats. For example, 500 sq ft ÷ 350 sq ft/gal × 2 coats = approximately 2.86 gallons. Always round up to the nearest quart or gallon when purchasing.

Is it better to buy gallons or quarts of paint?

For projects under 100 square feet per coat, quarts are often more economical. For larger rooms, buying gallons is more cost-effective. If your estimate comes out to just over a gallon, consider buying one gallon plus a quart rather than two full gallons to avoid excess.

How accurate is a paint calculator estimate?

Paint calculators provide a useful rough estimate, but actual paint usage varies based on wall texture, application method (brush vs. roller vs. sprayer), paint brand, and the color being covered. It's always wise to buy 10–15% extra to account for touch-ups and waste.

Can I use this calculator for exterior paint as well?

Yes — you can use this calculator for exterior surfaces by entering the total wall dimensions of your home's exterior. For exterior projects, also consider additional coats due to weather exposure, and factor in surfaces like siding, trim, and shutters separately for best accuracy.

More Math Tools