"What is the correct
amount of grip pressure when putting?"
According to Brad Faxon, you need to consider both grip pressure and arm pressure.
You want softer grip pressure and softer arm pressure so you can feel the weight of the putter head when you swing.
“When
I have spoken with Jack Nicklaus, he talked about how he felt like he had a two or three out of a scale of 10 for his grip pressure. I've always said three or four.
In both cases, it is considered light grip pressure. You're holding onto it hard enough that the putter's not going to twist out of your hand, but it's still soft.
But it’s nowhere near a 10.
Now, there's also something called arm pressure.
Do you feel your arm's tight sometimes?