District of Columbia is about 1,871 times smaller than Vietnam.

Vietnam is approximately 331,210 sq km, while District of Columbia is approximately 177 sq km, making District of Columbia 0.05% the size of Vietnam. Meanwhile, the population of Vietnam is ~103.8 million people (103.2 million fewer people live in District of Columbia).
Tip: This to-scale comparison of Vietnam vs. District of Columbia uses the Mercator projection, which distorts the size of regions near the poles.