Calculate exterior wall square footage for siding or paint from perimeter and wall height, adding gables and subtracting doors and windows, plus waste.

Rectangular walls plus equal triangular gables, minus openings. Blank options mean no additions, deductions or waste.

Optional settings

Blank means none. A positive count needs a base width and vertical rise.

Blank omits the package estimate.

Measuring a house’s floor area from outside? Use the House Area Calculator for length × width, with optional equal-sized floors and a finished-area percentage. For an irregular footprint, calculate non-overlapping rectangular sections separately and add their areas; calculate unequal floors separately. Outside dimensions include wall thickness, so this is a geometric estimate, not usable interior room area. Wall area for siding or paint is a different measurement.

Related Calculators

Exterior Square Footage Formula

For wall area, use perimeter × average rectangular height + triangular gables − openings. Waste changes the order area; blank optional entries mean zero, and blank package coverage omits packages. The separate Outdoor lot area mode uses the following formula for land not covered by building footprints.

ESF = TLA - BA

Variables:

  • ESF is the exterior square footage (e.g., sq ft)
  • TLA is the total land area of the lot (same area units as ESF)
  • BA is the total building footprint area (sum of building footprints on the lot, in the same area units as ESF)

To calculate the exterior square footage, subtract the building footprint area from the total land area. (If you need the footprint area of a rectangular building, you can compute it as BA = L × W.)

What is Exterior Square Footage?

Exterior square footage refers to the portion of a property’s lot that is outside of (and not covered by) building footprints. This can include elements such as the yard, driveway, patio, deck, porch, pool, and other outdoor features. It is often used in real estate and site planning because the amount of usable outdoor space can contribute to how a property is valued and used.

How to Calculate Exterior Square Footage?

The following steps outline how to calculate the Exterior Square Footage (ESF).

  1. First, determine the total land area of the lot (TLA).
  2. Next, determine the total building footprint area (BA). (If a building is rectangular, its footprint area can be calculated as L × W.)
  3. Next, gather the formula from above: ESF = TLA − BA.
  4. Finally, calculate the Exterior Square Footage (ESF).
  5. After inserting the values for TLA and BA into the formula and calculating the result, check your answer with the calculator above.

Example Problem:

Use the following variables as an example problem to test your knowledge.

Total land area (TLA) = 200 sq ft

Rectangular building footprint: L = 10 ft and W = 8 ft, so BA = 10 × 8 = 80 sq ft. Therefore, ESF = 200 − 80 = 120 sq ft.