District of Columbia is about 1.3 times bigger than Christmas Island.

Christmas Island is approximately 135 sq km, while District of Columbia is approximately 177 sq km, making District of Columbia 31% larger than Christmas Island. Meanwhile, the population of Christmas Island is ~2,205 people (599,518 more people live in District of Columbia).
Tip: This to-scale comparison of Christmas Island vs. District of Columbia uses the Mercator projection, which distorts the size of regions near the poles.