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Paint Calculator

Estimate how much wall paint you need in gallons or litres from room dimensions, doors, windows, coats, paint coverage, and waste.

Designed for four room walls. Ceilings, trim, primer, supplies, labour, and tax are not included.

🌎 Region

Choose US or Canada to use the appropriate measurement units and currency labels.

🏠 Room Size

Enter the inside length, width, and wall height of the rectangular room.

🚪 Doors & Windows

Enter openings that will not be painted so their area can be deducted from the walls.

Enter the approximate area of one door.

Enter the approximate area of one window.

🪣 Paint Settings

Enter the number of coats, product coverage, waste allowance, and optional paint price.

Use the coverage printed on the paint label or technical data sheet.

Use 5–15% for most projects to allow for touch-ups, surface texture, and application loss.

This calculator estimates finish paint for four walls. Actual coverage can vary with surface condition, porosity, paint product, colour change, roller or sprayer choice, and application method.

Estimated Paint Needed

0gallons

Whole-unit purchase estimate

0 gallons

This is a rounded paint volume, not the number of cans. Package sizes vary by product.

📐Wall Area0 sq ft
🚪Opening Deduction0 sq ft
🧱Paintable Area0 sq ft
🪣Area With Coats0 sq ft
➕Area With Waste0 sq ft

Estimated Paint Cost

$0

USD. Based only on the price per gallon entered above.

Results are planning estimates. Confirm the product's coverage and package sizes before purchasing paint.

Estimate disclaimer: This estimate is for planning purposes only. Actual costs may vary based on location, material prices, labor rates, taxes, fees, exchange rates, and project conditions.

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🧮 How Does the Paint Calculator Work?

The calculator first estimates the area of the four walls from room length, width, and height. It then subtracts the entered door and window areas, applies the number of paint coats, adds the waste allowance, and divides the total coverage area by the paint coverage rate you enter.

The final paint volume is shown before and after rounding to a whole gallon or litre. If you enter a paint price, the calculator also provides a simple material-cost estimate.

📐 Paint Quantity Formula

Four-wall area = 2 × (length + width) × height

Opening deduction = (doors × area per door) + (windows × area per window)

Paintable area = max(wall area − opening deduction, 0)

Coverage for all coats = paintable area × number of coats

Coverage with waste = coverage for all coats × (1 + waste % ÷ 100)

Paint needed = coverage with waste ÷ product coverage rate

🎯 What Can You Use the Estimate For?

  • 🎨 Estimate paint before shopping
  • 🏠 Compare different room dimensions
  • 🪣 Compare one-coat and multi-coat projects
  • 🚪 Account for unpainted doors and windows
  • 📦 Plan purchase quantity before choosing package sizes
  • 💰 Build a basic paint material budget

Use the result as a planning baseline. Real paint coverage depends on the actual paint and surface, so the product label and project conditions should take priority.

Worked Paint Example

This example calls the same calculatePaint() function as the interactive calculator, so the published result remains tied to the production calculation logic.

🇺🇸 Example: 12 ft × 10 ft Room

  • Room dimensions: 12 ft × 10 ft × 8 ft
  • Four-wall area: 352 sq ft
  • Openings: one 21 sq ft door and two 15 sq ft windows
  • Opening deduction: 51 sq ft
  • Paintable area: 301 sq ft
  • Coats: 2
  • Paint coverage: 350 sq ft per gallon
  • Waste allowance: 10%
  • Paint required before rounding: 1.892 gallons

Whole-unit planning quantity: 2 gallons

The values above are an example, not recommended room dimensions, paint coverage, waste, or price. Use the specifications for your actual project and paint product.

🇺🇸 US Paint Estimates

US mode uses feet, square feet, gallons, and USD. Enter the coverage stated for the paint product you plan to use and the current price per gallon when you want a material-cost estimate.

🇨🇦 Canada Paint Estimates

Canada mode uses metres, square metres, litres, and CAD. The underlying area and paint-volume logic is the same; only the measurement units and currency labels change.

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❓ FAQ

How much paint do I need for a room?

Measure the four walls, subtract the entered door and window areas, multiply the paintable area by the number of coats, apply the waste allowance, and divide by the coverage rate for the paint you plan to use.

Should I use one coat or two coats?

Use the number of coats recommended for your paint, surface, and colour change. Each additional coat increases the calculated coverage area proportionally.

Should I subtract doors and windows?

Yes, when those openings will not be painted. Enter the number of doors and windows and the approximate area of one of each so the calculator can subtract them from the four-wall area.

What paint coverage rate should I enter?

Use the coverage rate printed on the paint label or technical data sheet. Actual coverage can vary with surface texture, porosity, paint type, application method, and colour change.

How much extra paint should I allow for waste and touch-ups?

A 5% to 15% allowance is a practical planning range for many projects. Textured or porous surfaces, complicated rooms, application loss, and keeping paint for later touch-ups may justify a different allowance.

Does this calculator include primer, ceilings, or trim?

No. The calculator estimates finish paint for the four room walls. Primer, ceilings, trim, doors, baseboards, supplies, and labour should be estimated separately.

Does the whole-gallon or whole-litre result equal the number of paint cans?

No. The calculator rounds the required paint volume up to a whole gallon or whole litre. Actual package sizes vary, so divide the required volume by the package size you plan to buy and round up.

Is the estimated paint cost a contractor quote?

No. The cost estimate only multiplies the rounded paint quantity by the price per gallon or litre that you enter. It does not include tax, primer, supplies, labour, discounts, preparation work, or other project costs.

Calculation Scope and Review

The calculator uses a deterministic area-and-coverage calculation based on the values entered by the user. Room geometry, opening deductions, coats, waste, coverage, rounding, and optional material cost are calculated from the inputs shown on this page.

Real-world paint coverage is not fixed. Surface texture, porosity, preparation, paint formulation, colour change, and application method can change the amount of paint actually required. Use the manufacturer's current label or technical data sheet for product-specific coverage.

Calculation version
Paint Calculator V1
Last reviewed
August 2026
Maintained by
FigureNorth
Calculation type
Deterministic calculation with real-world planning inputs

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