The flag of Tonga has an aspect ratio of 1:2. It consists of two colors: red (#C60C30) and white (#FFFFFF). The flag is divided into two parts: a red field and a white canton in the upper hoist-side corner.

The white canton is a square with sides equal to half the height of the flag. Inside the canton, there is a red cross with arms that are 1/6th the width of the canton. The cross is centered within the canton, dividing it into four smaller squares.

The red field occupies the remaining area of the flag, extending from the right edge of the canton to the fly end and from the bottom edge of the canton to the bottom edge of the flag.