Northern Mariana Islands is about 8 times bigger than British Indian Ocean Territory.

British Indian Ocean Territory is approximately 60 sq km, while Northern Mariana Islands is approximately 464 sq km, making Northern Mariana Islands 673% larger than British Indian Ocean Territory.
Tip: This to-scale comparison of British Indian Ocean Territory vs. Northern Mariana Islands uses the Mercator projection, which distorts the size of regions near the poles.

Compare further: Northern Mariana Islands vs. British Indian Ocean Territory