A rat's teeth can grow up to 5-1/2 inches (14 cm) a year, but gnawing on
things keeps them shortened.

Rats are known for their prominent front teeth, which develop just over a
week after they are born and grow continuously throughout their lives. An
average rat’s teeth can grow from 4.5 (11.43 cm) to 5.5 inches (14 cm)
every year.