Triangle Area Calculator (Base × Height)

Triangle Area (½bh)

Enter any positive base length and the perpendicular height to work out the triangle’s area using the standard school formula. Useful for geometry homework and rough checks in either metric or imperial units—keep units consistent so the area is in square units of your choice.

Base length

Positive number; use the same units as height (cm, m, ft, in, etc.).

Perpendicular height

Altitude from the base to the opposite vertex, same units as base.

How it works

Enter any positive base length and the perpendicular height to work out the triangle’s area using the standard school formula. Useful for geometry homework and rough checks in either metric or imperial units—keep units consistent so the area is in square units of your choice.

The Formula

Area = (1/2) × base × height

Here “height” is the perpendicular distance from the base to the opposite vertex (not necessarily a slanted side length).

Worked Example

Worked example
Base = 8 cm and perpendicular height = 5 cm. Area = ½ × 8 × 5 = 20 cm². If you use metres instead, the same numbers give 20 m²—only the unit label changes.

Tips, Assumptions & Limitations

Height must be perpendicular to the chosen base—if you only know slant lengths, use another rule such as Heron’s formula instead.
Use the same unit for base and height so the area comes out in sensible square units (e.g. ft and ft → ft²).
Pick any side as the base; the matching height is the altitude to that base.

FAQ

Multiply base by the perpendicular height, then divide by two: Area = ½ × base × height. Our tool applies that formula once both values are positive numbers.

Use the perpendicular segment from the extended base line up to the opposite vertex. If you only know side lengths, a side-and-height tool may not be enough—consider Heron’s formula instead.

The maths is unitless until you label it. Enter base and height in the same unit (both metric or both imperial); the area is then in matching square units.

No. Heron uses all three side lengths. This tool needs one base and its matching altitude—faster when you already know those two measurements.