How to get percentage aggregation?

I don't find the way to get percentage in each bucket of an aggregation.
How does Elastic handle percentage calculation ?

Percentage of what?

Depending on what you need, a bucket script pipeline agg may work, although it has limitations.

If you just want to convert a raw double (0.01) to a percentage (1%), I'm afraid this isn't currently possible... you'll have to do the conversion in your application.