Triangle Square Footage Calculator
Calculate the area of a triangle using base × height (the standard formula) or three side lengths (Heron's formula). Useful for gables, attic spaces, and triangular gardens.
Triangle Area Calculator
Two formulas, two situations
Standard formula: area = (base × height) ÷ 2. The height MUST be measured perpendicular (90°) from the base to the opposite point. For a triangle with a 12-ft base and 8-ft perpendicular height: (12 × 8) ÷ 2 = 48 sq ft.
Heron's formula (when you only know the three sides): s = (a + b + c) ÷ 2. Then area = √(s(s-a)(s-b)(s-c)). The multi-shape calculator handles this automatically when you select "Triangle (3 sides)".
Real-world triangles
Roof gables are triangles. For a 30-ft-wide gable end with a roof peak 8.75 ft above the wall plate: (30 × 8.75) ÷ 2 = 131 sq ft of gable.
Attic floor cross-sections are triangles. The walkable floor in an unfinished attic with 8-ft trusses is a triangle - useful for estimating insulation or floor area for "knee-wall" build-outs.
Pro tips
Height is perpendicular, not slanted
For a triangle leaning to the right, the "height" isn't the right slanted edge - it's the straight-up distance from the base to the top point.
Use Heron's when you can't measure height
Triangular property corners are easier to measure as three side lengths than to find a perpendicular height. Use Heron's formula on the multi-shape calculator.
Right triangles are easiest
A right triangle has one 90° angle - the two legs adjoining that angle ARE the base and height. Just multiply legs and divide by 2.
Equilateral shortcut
For an equilateral triangle (all sides equal): area = (side² × √3) ÷ 4. A 10-ft equilateral triangle has area = (100 × 1.732) ÷ 4 = 43.3 sq ft.