How do you calculate the area of a triangle? To calculate the area of a triangle, multiply the height by the width (this is also known as the 'base') then divide by 2.

A KS3 Bitesize 11-14 Maths guide showing you how to prove the area of a triangle is half base × height.

Along the top line (height) of the triangle, the student has written 3.75, while the vertical line (base) is indicated as 1.875. These values mean the area of the triangle should be 3.5156.