To calculate the genealogical relationship between to people, compare the relationship to their common ancestor. It is often easiest to do this using a chart like the one below.
For example, you and your relative share a common ancestor, Emmet Wiscured. Emmet is your 4th great-grandfather. He is your cousin’s 3rd great-grandfather. To use the chart, start with you. Look across the headings at the top to find 4th great-grandparent. Then look down the left most column for your cousin’s relationship of 3rd great-grandparent. Find the point on the chart where the 4th great-grandparent column and 3rd great-grandparent row meet. This shows that you and your relative are 4th cousins once removed.