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Unit Conversion & Everyday Life

Paint Quantity Estimator

Estimate how much paint you need for a room from wall size, doors, windows, number of coats and the coverage on the label.

Your inputs

About 1.9 m² / 20 ft² for a standard interior door.

Often 10–12 m² per litre or 350–400 ft² per gallon.

Results

Paint needed

7.02 L

Cans to buy
3
Paintable area (one coat)
35.1 m²

≈Estimate based on the stated model and assumptions

Notes for this result

  • Porous, textured or dark-to-light surfaces may need more paint or a primer coat.

What this calculator does

Measure the walls, subtract openings, multiply by coats and divide by coverage. This tool also rounds up to whole cans.

Formula and method

Paintable area = perimeter × height − doors × door area − windows × window area Paint = area × coats ÷ coverage; Cans = ceiling(paint ÷ can size)

Worked example

Calculated by this tool with its default inputs:

Inputs

  • Units: Metric (m, m², litres)
  • Total length of walls to paint (room perimeter): 16
  • Wall height: 2.5
  • Doors: 1
  • Windows: 2
  • Area of one door: 1.9
  • Area of one window: 1.5
  • Coats: 2
  • Coverage per litre / gallon (from the label): 10
  • Can size (litres or gallons): 2.5

Results

  • Paint needed: 7.02 L
  • Cans to buy: 3
  • Paintable area (one coat): 35.1 m²

How to read the results

Buy a little extra for touch-ups; leftover paint from the same batch matches best.

Assumptions and limitations

  • Rough or porous surfaces use more paint.
  • Use metric or US units consistently.

Questions

How much does a litre cover?

Often 10–12 m² per coat; check the can.

Methodology and verification

Result type
Estimate based on the stated model and assumptions
Formula version
1.0
Automated verification
3 reference and validation test cases, checked against independently computed values. The site cannot be built if any of them fail.
Editorial review
Awaiting human editorial review. The explanation was drafted with AI assistance; the formula and examples are verified by the automated tests above.

Privacy

Everything you enter is calculated in this browser and is not sent to Numerith or anyone else. Inputs are added to a share link only if you choose to include them. Privacy policy