Singapore is about 4.1 times bigger than District of Columbia.

District of Columbia is approximately 177 sq km, while Singapore is approximately 719 sq km, making Singapore 306% larger than District of Columbia. Meanwhile, the population of District of Columbia is ~601,723 people (5.3 million more people live in Singapore).
Tip: This to-scale comparison of District of Columbia vs. Singapore uses the Mercator projection, which distorts the size of regions near the poles.