Three Point Zero Three Centimeters, Three Centimeters, Three Point Oh Three Centimeters
This measurement also refers to a specific measurement, a "sun", which is about 3.03 centimeters. You'll hear it brought up from time to time to measure things, though usually with more traditional Japanese items.
The reading is the same as the kanji! Congrats! Now to remember it's three point zero three centimeters.
1 sun is 1/10th of 1 shaku, which is approximately 3.03 centimeters.