Index memory quota allocation

How to calculate required Index service memory quota? In documentation, , instructions are not clear. The example also tells about disk sizing. What we need is RAM sizing.
This is for Couchbase CE v 5.0

@manish_bansal for Standard GSI, please try creating your indexes on a subset of data and from that, you can extrapolate to find the total usage. And from ratio of working set to total data set, memory quota required can be derived. You can change the memory quota assigned to indexer at any point of time.