District of Columbia is about 2.6 times smaller than Northern Mariana Islands.

Northern Mariana Islands is approximately 464 sq km, while District of Columbia is approximately 177 sq km, making District of Columbia 38.15% the size of Northern Mariana Islands. Meanwhile, the population of Northern Mariana Islands is ~51,475 people (550,248 more people live in District of Columbia).
Tip: This to-scale comparison of Northern Mariana Islands vs. District of Columbia uses the Mercator projection, which distorts the size of regions near the poles.