Enrichment · Passion Projects · Home projects

Two coats,
one bedroom, and
no third trip to the store.

Measure each wall and count the doors and windows. The calculator gives the area to paint, the gallons it takes and exactly what to buy.

Count the paintWhat you get

The paint calculator

The worked example is a made-up 12 × 11 ft bedroom with 8 ft ceilings, one door and two windows. Nothing you type leaves this browser.

Loading the calculator. If nothing appears, turn on JavaScript.

What you get

Enrichment · Passion ProjectsFree

What you finish with
The paintable area, the gallons needed and what to buy in gallons and quarts, with the leftover. It prints as a summary and downloads as a spreadsheet.
Who it is for
Families planning a paint job, students moving into their own place, and geometry classes working with area.
Format
Browser calculator for a phone, tablet or computer, by touch or keyboard. Up to 30 walls. Prints a summary; downloads a spreadsheet (.csv); export and import a file.
Access
Free. No account, no sign-in and nothing to install. Everything you type stays in this browser; nothing is sent to Caveat.
Where it lives
The Passion Projects space in Caveat Enrichment.
Support
Questions, a correction or a request: team@caveatacademic.com.

How to use it

  1. Measure each wall's length and height and add it.
  2. Count the doors and windows.
  3. Set the coats and the coverage from the can.
  4. Read what to buy.
  5. Print the summary for the store.

Count the paint

How the paint is worked out

Area, less openings, times coats.

The worked example: a bedroomWalls368 sq ft(12 + 11 + 12 + 11) × 8Less openings318 sq ft− 1 door × 20 − 2 windows × 15× 2 coats ÷ 3501.82 galcoverage on the canBuy2 gallonsrounded up to quartsThe worked example: a bedroomWalls368 sq ft(12 + 11 + 12 + 11) × 8Less openings318 sq ft− 1 door × 20 − 2 windows × 15× 2 coats ÷ 3501.82 galcoverage on the canBuy2 gallonsrounded up to quarts
The walls of a room add up to the perimeter times the height. Doors and windows come off; coats multiply.

The arithmetic

Each wall is length × height. Doors (about 20 sq ft) and windows (about 15 sq ft) are taken off. Gallons are the area × coats ÷ the coverage per gallon on the can. Paint comes in quarts and gallons (4 quarts to the gallon), so the amount is rounded up to quarts, and three quarts become a gallon because they usually cost about the same.

What changes coverage

Rough texture, bare drywall and a big colour change soak up more paint; primer first can save a coat. Ceilings and trim are usually a different paint; measure them as their own job. Ventilate the room and keep leftover paint sealed for touch-ups.

Sources

  1. U.S. Environmental Protection Agency. Volatile organic compounds and indoor air quality: ventilation when painting (epa.gov).
  2. National Institute of Standards and Technology. Handbook 44, appendix C: 4 quarts to the US gallon (nist.gov).
  3. Cooperative Extension (land-grant universities). Home painting guides: estimating paint and preparing surfaces (state extension services).
  4. OpenStax. Prealgebra 2e, section 9.4: area of rectangles (openstax.org).

The worked example is made up. Check the coverage on your can. Your figures stay in this browser. Support: team@caveatacademic.com.