Guinea-Bissau is about 602 times bigger than British Indian Ocean Territory.

British Indian Ocean Territory is approximately 60 sq km, while Guinea-Bissau is approximately 36,125 sq km, making Guinea-Bissau 60,108% larger than British Indian Ocean Territory.
Tip: This to-scale comparison of British Indian Ocean Territory vs. Guinea-Bissau uses the Mercator projection, which distorts the size of regions near the poles.
Compare further: Guinea-Bissau vs. British Indian Ocean Territory