Triangle Square Footage Calculator
Enter the base and perpendicular height of any triangle. The calculator returns the area using the
formula (base × height) / 2 — works for every type of triangle.
Tip: If you only have the diameter, divide by 2 to get the radius.
L-shape = two rectangles sharing a corner.
Add one row per rectangle and we'll sum them.
Triangle Area Formula
The classic formula is Area = (base × height) / 2, where height is the perpendicular
distance from the base to the opposite vertex, not the length of the other side.
- Base 10 ft, Height 8 ft → (10 × 8) / 2 = 40 sq ft
- Base 14 ft, Height 9 ft → (14 × 9) / 2 = 63 sq ft
- Base 20 ft, Height 15 ft → (20 × 15) / 2 = 150 sq ft
Finding the Height of a Triangle
For a right triangle, the two legs meeting at the right angle are the base and height. For other triangles, drop a perpendicular line from the top vertex straight down to the base — that's your height. For a gable end or trusses, the height is measured from the base of the truss to the peak.
Common Uses for Triangle Square Footage
- Gable walls — paint, siding, or drywall for a gable end is a triangle.
- Attic floors — often partially triangular where the roof slopes meet the floor.
- Garden beds — landscapers use triangle area for sod and mulch.
- Roofing — each roof plane is split into rectangles and triangles for shingle estimation.
Frequently Asked Questions
How do I calculate the square footage of a triangle?
Multiply the base by the perpendicular height and divide by 2. A 14 ft × 9 ft triangle is (14 × 9) / 2 = 63 sq ft.
What if I don't know the perpendicular height?
For a right triangle, height is one of the two legs. For other triangles, draw a line from the apex straight down to the base; that's the height.
Does this formula work for scalene and isosceles triangles?
Yes. As long as you use the perpendicular height (not the slant length), (base × height) / 2 works for every triangle.