San Marino is about 2.9 times smaller than District of Columbia.

District of Columbia is approximately 177 sq km, while San Marino is approximately 61 sq km, making San Marino 34.46% the size of District of Columbia. Meanwhile, the population of District of Columbia is ~601,723 people (567,041 fewer people live in San Marino).
Tip: This to-scale comparison of District of Columbia vs. San Marino uses the Mercator projection, which distorts the size of regions near the poles.