Hgrad relation to a triangle internal angles in mmg2d

Hello there!
I’m using mmg2d and I’m having problem understanding how to setup hgrad parameter.
Starting from a tris mesh I need to have it remeshed so as the tris internal angles are about a specific quality value, say 25 degrees.
How to do I set the hgrad parameter for this?
In the docs hgrad is reported as:

1/h <= e1/e2 <= h

h = hgrad
e1 = edge1
e2 = edge2

How to turn this identity into something related to degrees? Or how to prescribe an equivalent quality goal?
Thank you