Pitcairn Islands is about 8,593 times smaller than California.

California is approximately 403,882 sq km, while Pitcairn Islands is approximately 47 sq km, making Pitcairn Islands 0.01% the size of California. Meanwhile, the population of California is ~37.3 million people (37.3 million fewer people live in Pitcairn Islands).
Tip: This to-scale comparison of California vs. Pitcairn Islands uses the Mercator projection, which distorts the size of regions near the poles.