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Paint Calculator

Estimate how much paint you need from room dimensions or a direct paintable area, with adjustable coverage and coats.

Choose a calculation

Calculate from room length, width and wall height, in feet.

Result

How to Use

  1. Choose room dimensions or a direct paintable area, in feet or meters, from the options above the form.
  2. For room dimensions, enter length, width and wall height — the calculator works out the wall area (all four walls) automatically.
  3. Deduct the total area of doors, windows and other openings you won't paint, and set how many coats you're applying.
  4. Adjust the coverage rate to match your paint's label if it differs from the default, and add a waste allowance if you want a buffer.
  5. The result shows the exact quantity needed and a practical purchase quantity rounded up to a whole can.

Formula

Room wall area
gross_wall_area = 2 × (length + width) × wall_height, then subtract openings
Paint needed
exact = (paintable_area × coats ÷ coverage_rate) × (1 + waste% ÷ 100)
Practical amount
practical = round exact UP to the next whole gallon or liter

Worked Example

A 12 ft by 10 ft room with 8 ft walls, 20 sq ft of doors and windows, 2 coats.

  1. Gross wall area: 2 × (12 + 10) × 8 = 352 sq ft
  2. Paintable area: 352 − 20 = 332 sq ft
  3. Exact paint needed: (332 × 2) ÷ 350 = 1.90 gallons
  4. Practical purchase quantity: round 1.90 up to 2 gallons

Result: Paintable area: 332 ft² (2 coats) / Exact paint needed: 1.9 gal / Practical purchase quantity: 2 gal

About This Tool

What this tool does

This calculator estimates how much paint a job needs, either from a room's dimensions (working out the wall area for you) or from a paintable area you already know, accounting for coats, openings to skip, and an optional waste allowance.

When to use it

Use it before a painting project to estimate how many cans to buy, comparing your paint's actual labeled coverage against the default assumption.

What the result means

The exact quantity is the precise calculated amount; the practical purchase quantity rounds that up to a whole gallon or liter, since paint is sold in whole cans — actual retail can sizes vary by brand and region, so check what's available before buying.

Assumptions & limitations

The default coverage rate (350 sq ft/gallon or 10 sq m/liter) is a commonly cited average for a single coat of interior wall paint — actual coverage varies significantly by paint product, surface texture, and application method (roller vs. sprayer vs. brush), so always check your specific product's label and adjust the Coverage field to match. This tool estimates paint quantity only; it does not provide ventilation, VOC, disposal, or other hazardous-material safety guidance — follow your paint manufacturer's safety information for that.

Frequently Asked Questions

How much paint do I need for a room?
Work out the total wall area (perimeter × height), subtract doors and windows, multiply by the number of coats, then divide by your paint's coverage rate per gallon or liter. This calculator does that automatically from your room dimensions.
Why does the calculator round up the practical quantity?
Paint is sold in whole cans, so an exact calculation of "1.9 gallons" still means buying 2 gallons in practice. The exact figure is shown too, in case you're comparing against a specific can size or estimating cost precisely.
What if my paint's coverage is different from the default?
Check the coverage rate printed on your paint can (usually in square feet per gallon or square meters per liter) and enter that exact number in the Coverage field — the default is just a common average, and real coverage varies by product and surface.

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