Measure and MendStart measuring

Paint

Exterior siding paint

Exterior spread rate has a wider cited range than the typical interior figure. Siding profile, bare or weathered areas, application losses, and coating choice matter, so this is a purchase-planning range rather than a promise of coverage.

First answer

Measure each exterior face, subtract large unpainted openings, multiply by coats, and divide by the general exterior range of 400 to 250 square feet per gallon.

Run the calculator

Formula or decision rule

sum of exterior face areas − excluded openings; then × coats × allowance factor ÷ 400 to 250 ft²/gal
  • Calculate gables separately instead of treating them as rectangles.
  • Keep trim, doors, and siding in separate coating calculations.
  • Use the selected exterior product label when available.

Exterior face geometry

Exterior face geometry
ShapeArea formulaTypical use
Rectanglewidth × heightwall below eaves
Trianglebase × height ÷ 2simple gable
Openingwidth × heightunpainted door or window
Coverage range250–400 ft²/galgeneral exterior planning

Work through the project

  1. Measure by elevation

    Keep front, rear, and side faces separate so gables and additions remain visible in the worksheet.

  2. Inspect before calculating

    Mark peeling, bare, damaged, or wet areas because preparation and primer needs cannot be inferred from square footage.

  3. Match the coating system

    Confirm substrate compatibility, primer, spread rate, temperature range, and dry-time instructions on the chosen labels.

Safety and scope

  • Use appropriate fall protection and professional help for elevations you cannot reach safely.
  • Do not sand or scrape suspect lead coating until the applicable U.S. or Canadian guidance is followed.

Sources and scope

Source links reviewed July 16, 2026. A review date is not the document's publication date.

  1. Sherwin-Williams: Exterior Painting How-TosNorth America · manufacturer guide

    Use the selected coating label when it provides a more specific spread rate.

  2. National Institute of Standards and Technology: NIST Guide to the SI, Appendix B — Conversion FactorsUnited States · government standard

    Code retains exact defining constants where NIST identifies an exact relationship.

  3. U.S. Environmental Protection Agency: Steps to Lead Safe Renovation, Repair and PaintingUnited States · government guide

    Lead rules and certified-contractor requirements may apply; this site does not replace regulatory guidance.

  4. Health Canada: Lead-based paintCanada · government guide

    Paint history is a screening clue, not a laboratory identification.