This is a list of Interstate Highways in the U.S. state of California that have existed since the 1964 renumbering.

Lengths for each state route were initially measured as they were during the 1964 state highway renumbering (or during the year the route was established, if after 1964) based alignment that existed at the time, and do not necessarily reflect the current mileage.

Portions of some routes have been relinquished to or are otherwise maintained by local or other governments, and may not be included in the length listed below.

Several routes are broken into non-contiguous pieces, and their lengths may not reflect the overlaps that would be required to make them continuous.

When a highway is broken into such segments, the total length recorded by Caltrans only reflects those non-contiguous segments, and does not include those overlaps that would be required to make the route continuous.