Use the formula for triangle area: Area = 1/2 × base × height
Rearrange the formula to solve for base: base = (2 × Area) / height
Measure or identify the triangle’s area
Measure or identify the perpendicular height to the chosen base
Substitute the area and height into the formula
Calculate the base length
If the triangle is isosceles or equilateral, the base is the side not equal to the other equal side(s)
If only side lengths are known, use trigonometry or Heron’s formula to find the area first, then solve for the base