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Paint Calculator

Use this paint calculator to estimate wall area in square feet or square meters, gallons of paint needed, and paint cost before buying supplies.

Method and assumptions documentedFree toolSource note included

Live calculator

Paint calculator

Paintable area292 sq ft

Wall area minus doors and windows; 292 sq ft / 27.1 sq m.

Paint needed1.75 gallons

1.67 raw gallons, rounded to the nearest quart.

Estimated paint cost$66.50

Rounded gallons multiplied by price per gallon.

Material estimates need field measurements and a waste allowance. Supplier coverage, cuts, breakage, compaction, and local installation requirements can change the order quantity.

Quick answer

Paint Calculator: what it calculates

Paint Calculator estimates paintable wall area, gallons, coats, and paint cost from perimeter, wall height, openings, coverage, and price per gallon.

ResultPaint needed
InputsFeet or meters, Room perimeter, Wall height, Doors/windows area, Coats, Coverage
FormulaPaint calculator formula

Formula

Paint calculator formula

Paintable area = perimeter x wall height - doors and windows; gallons = paintable area x coats / coverage per gallon

Coverage varies by paint, surface texture, color change, primer, and application method.

How to use

Steps

  1. Choose feet or meters for the wall measurements.
  2. Enter the room perimeter or total wall length and wall height.
  3. Subtract estimated door and window area in square feet or square meters.
  4. Enter number of coats and coverage per gallon.

Example

Sample calculation

Perimeter44 ft
Wall height8 ft
Doors/windows60 sq ft / 5.57 sq m
Paint needed1.75 gallons

Calculator use

Best for

  • Estimating paintable wall area, gallons, coats, and paint cost before buying paint.
  • Checking how doors, windows, wall height, and number of coats change the gallons needed.
  • Planning interior wall paint before comparing product coverage, primer needs, and container sizes.
  • Creating a first material estimate before adding tape, rollers, brushes, drop cloths, and labor elsewhere.

Before relying on it

Check first

  • Using a generic coverage number when the paint can, surface texture, color change, or primer need says otherwise.
  • Forgetting ceilings, trim, doors, closets, accent walls, or repairs if they are part of the same job.
  • Buying exact calculated gallons without rounding to real container sizes or saving touch-up paint.
  • Assuming one coat is enough for new drywall, stains, patched walls, or strong color changes.

Details

What to know before using the result

Paintable areaSubtract openings

The calculator subtracts door and window area from wall area before multiplying by coats.

Coverage inputUse the can label

Coverage varies by product, surface texture, color change, primer, and application method, so the paint label is the best input.

Buying amountRound up containers

Paint is sold in set container sizes. Rounding up reduces the risk of running short and leaves extra for touchups.

Source notes

References used for this calculator

Sherwin-WilliamsPaint calculator guidance notes that one gallon typically covers about 350 to 400 square feet, depending on surface and coverage.

Benchmarks

How to read the result

One gallon: About 300 - 400 sq ft.

Actual coverage depends on paint quality and wall texture.

Two coats: Common.

Often needed for stronger color changes or even coverage.

Primer: Separate check.

Primer may be needed on new drywall, stains, or major color changes.

Calculator accuracy

Methodology and assumptions

Formula

Paintable area = perimeter x wall height - doors and windows; gallons = paintable area x coats / coverage per gallon

Inputs used

Feet or meters, Room perimeter, Wall height, Doors/windows area, Coats, Coverage

Limitations

Home-material calculators estimate quantity and cost from visible dimensions and coverage assumptions. They do not replace field measurement, installer guidance, structural design, permits, or code review.

Review record

Catalog QA baseline on June 6, 2026. This date marks the catalog-wide automated and editorial QA baseline, not a tool-specific expert review.

Cite this page

Toolkit Shelf. Paint Calculator. https://toolkitshelf.com/tools/paint-calculator

FAQ

Common questions

How do I calculate how much paint I need?

Multiply wall area by the number of coats, then divide by coverage per gallon.

Should I subtract doors and windows?

Yes. Subtracting doors and windows gives a better estimate of paintable wall area.

Why round paint up?

Paint is sold in containers, and extra paint helps with touchups and coverage differences.

Why should I add a material buffer?

Cuts, waste, damaged pieces, uneven surfaces, pattern matching, delivery limits, and field measurements can all make the exact calculated amount too low.

Can this replace a contractor quote?

No. Use it for planning quantities and budgets. Labor, permits, code, site conditions, disposal, access, and contractor scope can change the real project cost.