Guam is about 1,199 times smaller than Afghanistan.

Afghanistan is approximately 652,230 sq km, while Guam is approximately 544 sq km, making Guam 0.08% the size of Afghanistan. Meanwhile, the population of Afghanistan is ~43.8 million people (43.7 million fewer people live in Guam).
Tip: This to-scale comparison of Afghanistan vs. Guam uses the Mercator projection, which distorts the size of regions near the poles.
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