Cook Islands is about 3.9 times bigger than San Marino.

San Marino is approximately 61 sq km, while Cook Islands is approximately 236 sq km, making Cook Islands 287% larger than San Marino. Meanwhile, the population of San Marino is ~34,682 people (26,554 fewer people live in Cook Islands).
Tip: This to-scale comparison of San Marino vs. Cook Islands uses the Mercator projection, which distorts the size of regions near the poles.