Unity Health Math Problem

I’m making a platforming game, the character has a base amount of Health Points which is 50. I want to use the remaining percent amount of health to affect the grow size of a particle. I have already figured out how to modify the size growth of my particle, but I seem to be missing something very easy when it comes to my math.

I want to make it so, the lower the HP, the bigger the size of the particle will get with a maximum of 2,5.

Example using fictional informations:
10(%HP) (some math) = 2.5
90(%HP) (same math) = 0.8

Somehow I’m forgetting some fundamentals… Sorry if this is a dumb question, but I’m really puzzled by this.

If you have any idea which could help me out even though it is not the perfect answer, I won’t mind.

Thanks in advance.

float baseHP = 50.0f;
float maxSize = 2.5f;
float particleSize = Mathf.Lerp(maxSize, 0, actualHP / baseHP);