British Indian Ocean Territory is about 7 times smaller than Saint Helena, Ascension, and Tristan da Cunha.

Saint Helena, Ascension, and Tristan da Cunha is approximately 394 sq km, while British Indian Ocean Territory is approximately 60 sq km, making British Indian Ocean Territory 15.23% the size of Saint Helena, Ascension, and Tristan da Cunha.
Tip: This to-scale comparison of Saint Helena, Ascension, and Tristan da Cunha vs. British Indian Ocean Territory uses the Mercator projection, which distorts the size of regions near the poles.
Compare further: British Indian Ocean Territory vs. Saint Helena, Ascension, and Tristan da Cunha