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

District of Columbia is approximately 177 sq km, while Christmas Island is approximately 135 sq km, making Christmas Island 76.27% the size of District of Columbia. Meanwhile, the population of District of Columbia is ~601,723 people (599,518 fewer people live in Christmas Island).
Tip: This to-scale comparison of District of Columbia vs. Christmas Island uses the Mercator projection, which distorts the size of regions near the poles.