Over the years, scientists have attempted to classify curliness by measuring different parameters of the hair fiber. One of the most popularly cited studies is by the L'Oréal Institute for Ethnic Hair and Skin Research, which organized hair shapes into eight types by studying 2,449 subjects from 22 countries and five continents. Measuring curl diameter and curl index (the ratio of the stretched length of the hair to its length at rest), and counting waves and twists from each participant's hair, the scientist came up with a system assigning a number to hair type from 1-4. "The higher the number, the curlier the hair and the tighter the coil,"

This guide is a great starting point for finding the curl type that best resembles yours (note that this list omits type 1, as it refers to straight hair). To find out, you may want to sacrifice a few hair strands by plucking them out off your head while hair is still wet. Lay them flat against a white surface and watch them take their natural shape while they air-dry. You may identify with a few different patterns, as all hair doesn't necessarily contain the same type of curl consistently throughout.

https://www.goodhousekeeping.com/beauty/hair/a32733411/curl-hair-types/

For more detailed info click the above link to the page from Good Housekeeping