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Calculator Answers

Paint Calculator

Blake Boege
Written by Blake Boege · Founder, Calculator Answers

A paint calculator is a home improvement planning utility that estimates the volume of paint required to cover the walls or ceilings of a room. By entering room dimensions, the number of doors and windows (which are subtracted from the total surface area), and the desired number of paint coats, the calculator determines the total square footage and outputs the necessary paint volume in gallons or liters. DIY homeowners, professional decorators, and painters use this tool to purchase the correct amount of material and prevent unnecessary product waste.

Enter wall length, wall height, the number of walls, and how many coats you plan to apply. Subtract doors and windows, add an optional ceiling, and the calculator returns the total paintable area and how many gallons to buy.

See also: Tile Calculator, Drywall Calculator, and Wallpaper Calculator.

Quick Answer

Estimate the amount of paint needed for your room. Enter wall dimensions, doors, windows, and coats to calculate the required paint volume in gallons.

ft

Average length of each wall. · e.g. 12

ft

Floor to ceiling. · e.g. 9

Most rooms have 4 walls. · e.g. 4

Two coats is the most common spec. · e.g. 2

sq ft

Check the can; 350 is a common starting point. · e.g. 350

Each door subtracts 20 sq ft. · e.g. 1

Each window subtracts 15 sq ft. · e.g. 2

sq ft

Add the ceiling's square footage if you're painting it too. · e.g. 120

Coverage varies by paint type, surface texture, primer use, and color change. Buy a little extra for touch-ups.

Paint estimate

764 sq ft over 2 coats

3 gal

Exact: 2.18 gallons

Wall area432 sq ft
Door + window deductions-50 sq ft
Paintable area382 sq ft
Exact gallons2.18

Plan to buy at least 3 gallons. A small extra container for touch-ups is a good call, especially in high-traffic rooms.

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Examples

12 ft × 9 ft × 4 walls, 1 door, 2 windows, 2 coats

≈ 764 sq ft of paint, ~2.18 gallons, buy 3

Long hallway: 30 ft × 9 ft × 2 walls, 1 door

≈ 520 sq ft × 2 coats = 1,040 sq ft, ~2.97 gallons, buy 3

Small bathroom: 8 ft × 8 ft × 4 walls, 1 door

≈ 236 sq ft × 2 = 472 sq ft, ~1.35 gallons, buy 2

How it works

Wall area is length × height × number of walls. Door and window cutouts come off the top, and any ceiling area you choose to paint is added back. Multiply the result by coats to get the total square feet of paint, then divide by the can's coverage rating to get gallons.

Paintable area · walls − doors − windows + optional ceiling

Gallons · (paintable area × coats) ÷ coverage per gallon

Defaults: door = 20 sq ft · window = 15 sq ft · coverage = 350 sq ft/gal. Actual coverage varies by paint, texture, primer, and color change.

Paint needed by paintable area

The paint calculator above handles your exact room dimensions and deductions. The table below provides standard coverage estimates based on paintable area (excluding doors/windows) using a standard coverage rate of 350 sq ft per gallon.

Paintable Area1 Coat (Exact)1 Coat (To Buy)2 Coats (Exact)2 Coats (To Buy)
200 sq ft0.57 gal1 gal1.14 gal2 gal
400 sq ft1.14 gal2 gal2.29 gal3 gal
600 sq ft1.71 gal2 gal3.43 gal4 gal
800 sq ft2.29 gal3 gal4.57 gal5 gal
1,000 sq ft2.86 gal3 gal5.71 gal6 gal
1,200 sq ft3.43 gal4 gal6.86 gal7 gal

Worked example

Let's calculate the paint needed for a standard room that is 12 ft long, 9 ft high, has 4 walls, 1 door, and 2 windows, with a 2-coat paint job:

  • Gross wall area: 12 ft length × 9 ft height × 4 walls = 432 sq ft.
  • Deductions: 1 door (20 sq ft) + 2 windows (2 × 15 sq ft = 30 sq ft) = 50 sq ft.
  • Net paintable area: 432 sq ft − 50 sq ft = 382 sq ft.
  • Total paint coverage: 382 sq ft × 2 coats = 764 sq ft of paintable surface.
  • Gallons needed: 764 sq ft ÷ 350 sq ft/gallon = 2.18 gallons.
  • Order size: Rounding up to the nearest whole gallon, you should buy 3 gallons.

Common mistakes

  • Forgetting the second coat. Applying a single coat of paint often leaves patches or existing colors showing through, especially on textured walls. Be sure to calculate for two coats.
  • Not deducting doors and windows. Skipping deductions for doors and windows can lead to overbuying paint by up to 15-20% for standard rooms.
  • Using a single coverage rate. While 350 sq ft/gallon is standard, rough plaster, textured masonry, or unprimed drywall will absorb more paint, lowering coverage to 250–300 sq ft/gallon.
  • Forgetting that ceiling area is separate. Ceilings require a different calculation (room length × width) and often use a flat or specialty ceiling paint rather than the wall paint.

Related home measurement calculators

Sources: Typical paint manufacturer specifications cite coverage rates of 300–400 sq ft per gallon. Actual coverage rates vary by surface porosity, texture, and brand. Last reviewed: June 2026.

Related Calculators

More tools from Home

Tile CalculatorEstimate the number of tiles needed for a floor, wall, backsplash, or shower from area dimensions, tile size, and a waste allowance.Drywall CalculatorEstimate the drywall sheets needed for a room from wall dimensions, sheet size, door and window deductions, and a waste allowance.Wallpaper CalculatorCalculate the number of wallpaper rolls needed from wall length, height, count, and door/window deductions. Adjusts for pattern-repeat waste and a general waste allowance, with optional cost estimate.Square Footage Calculator – Sq Ft for Any RoomCompute square feet, square yards, square meters, and acres with this free square feet calculator. Enter length and width in feet or inches for quick area conversion.

Frequently asked questions

Paint coverage is estimated by calculating the total wall area, subtracting doors and windows, and multiplying by the number of coats. This total square footage is then divided by the coverage rate per gallon (typically 350 sq ft) to find the required volume.

One gallon of paint typically covers between 300 and 400 square feet, though this calculator defaults to a standard estimate of 350 square feet. Coverage can vary depending on surface texture, porosity, and color changes.

You generally need two coats of paint for a professional, durable finish and proper color saturation. One coat may suffice when refreshing an identical color on a clean, primed wall, while three coats might be needed for extreme color transitions.

Yes, you should subtract doors and windows to avoid overbuying paint. The standard deduction is 20 square feet per average door and 15 square feet per average window.

You will need approximately 2 to 3 gallons of paint for a standard 12x12 room with 9-foot ceilings and two coats. This estimate assumes a gross wall area of 432 square feet and accounts for normal deductions like one door and two windows.

No, primer is not included in paint coverage estimates as it is a separate product applied before painting. Primer seals porous surfaces and ensures paint adheres properly, meaning you will need to buy primer separately if painting raw drywall or making a major color change.

You will need about 1 gallon of flat ceiling paint for every 350 square feet of ceiling area. To calculate your ceiling's square footage, multiply the room's length by its width.

Yes, you should purchase about 10% more paint than estimated to account for touch-ups, spills, and future repairs. Buying one extra quart or gallon ensures you have paint from the same color-matched batch for any necessary fixes.

Textured walls can reduce paint coverage by up to 20% to 25% because the uneven surface has more actual area than a flat plane. If you have stucco, brick, or heavy plaster walls, you should lower your estimated coverage per gallon to 250–300 square feet.

Yes, the color change determines whether you will need extra coats or a tinted primer. Moving from a dark wall color to a light one typically requires a primer coat plus two coats of paint to prevent show-through.

You can use the same paint color, but you should typically use a different gloss level (sheen) such as semi-gloss or gloss for trim and baseboards. Trim paint is formulated to be more durable and easier to clean than standard wall paint.

Opened paint can last up to 10 years if stored in a cool, dry place in an airtight container. Be sure to seal the lid tightly and avoid storing paint where temperatures drop below freezing, which ruins the emulsion.