An author's research impact is commonly measured by:
h-index was proposed by Professor Jorge E. Hirsch in 2005.
Calculation
The h-index is calculated by counting the number of publications (h) by a scholar have been cited for at least h times. It measures both productivity (number of publications) and impact (number of citations) in one index.
For example, an h-index 33 means that the scholar has published at least 33 papers that have each been cited at least 33 times.
Source: https://en.wikipedia.org/wiki/H-index