Isosceles triangle
Area and perimeter, with the formula worked through and a drawing to scale.
Result
- Area
- 12 sq ft
- = 12 sq ft · 1.1148 m²
- Perimeter
- 16 ft
- = 16 ft · 4.8768 m
- Height h
- 4 ft
- Apex angle
- 73.7398°
- Base angles
- 53.1301°
The working
Area: A = b × h ÷ 2, h = √(s² − (b/2)²)
Perimeter: P = b + 2s
h = √(5² − (6/2)²) = 4 A = b × h ÷ 2 = 12 P = b + 2s = 16
Values in feet; areas in sq ft.
About the isosceles triangle
Two equal sides — a gable end. The height drops straight down the middle, splitting it into two right triangles.
Every formula on this site is explained step by step in Learn: area and perimeter.
Other shapes
Square Rectangle Parallelogram Rhombus Trapezoid (trapezium) Kite Triangle — three sides Triangle — base and height Right triangle Equilateral triangle Triangle — two sides and the angle between Circle Semicircle Quarter circle Sector (pie slice) Circular segment (arch) Ring (annulus) Ellipse (oval) Regular polygon (pentagon, hexagon, octagon…) L-shape Any polygon — by corner points