San Diego is about 2,778 times smaller than Democratic Republic of the Congo.

Democratic Republic of the Congo is approximately 2,344,858 sq km, while San Diego is approximately 844 sq km, making San Diego 0.04% the size of Democratic Republic of the Congo.
Tip: This to-scale comparison of Democratic Republic of the Congo vs. San Diego uses the Mercator projection, which distorts the size of regions near the poles.
Compare further: San Diego vs. Democratic Republic of the Congo