Triangle Area Calculator
By Santaji GadepatilinUpdated October 27, 2026
Area (cm²) vs Height (cm) — other inputs held at your current values.
How to use this calculator
Enter the base and height to get the area. You can also enter the area and one dimension to find the other — useful when a plan gives you the area and the base.
The formula
A = ½ × b × h
The height is the perpendicular distance from the base to the opposite corner — not the length of a sloping side.
Why one half?
Any triangle is exactly half of a parallelogram with the same base and height. A parallelogram’s area is base × height, so the triangle gets half of that.
Worked example
A triangular garden bed has a 4 m base and is 2.5 m deep (measured straight out from the base).
A = ½ × 4 × 2.5 = 5 m²
At 40 litres of compost per m², you would need 200 litres.
Which side is the base?
Any side can be the base, as long as you use the height measured to that side. All three choices give the same area.
Right triangles
In a right triangle, the two sides that meet at the right angle are a base and its height. A 3-4-5 triangle has an area of ½ × 3 × 4 = 6. Use the Pythagorean theorem calculator to find a missing side first.
Frequently asked questions
What is the formula for the area of a triangle?
Area = ½ × base × height. A triangle with a 12 cm base and 8 cm height has an area of 48 cm².
Does the formula work for every triangle?
Yes, as long as the height is measured at a right angle to the chosen base. For obtuse triangles, the height may fall outside the triangle.
How do I find the height from the area?
Height = 2 × area ÷ base. Press × on Height, then type the area.