The size of your goldfish will have something to do with how much you feed.
A 3-4 inch fish needs more than a once inch fish 1.
I feed 1-2 pinches of flake food and 3-4 soaked floating pellets by hand in the morning.
Usualy, thats what he can consume in 3-5 minuets
A pea in the middle of the day, deshelled & not salted.
And 1-2 pinches of flake food, with several small soaked sinking crumbly things.
Again, what he normaly can consume in 3-5 minuets.
I have wondered if I was overfeeding, but was told no.
(Someone step up and correct me if I'm wrong.)
I treat Glaze to live food, mosquito larve mostly, because its summer and the larve is free
Feed your goldfish as much as he can eat in 3-5 minuets 1-2 times a day and go from there.
If your water quality is hard to maintain, feed less. Ect.
There are alot of factors that can help guide you in feeding your fish.
Like Fishy Wishey said, in getting to know your fish you will learn how much to feed.
Goldfish are oportunistic eatters, and, making you believe that they are always hungry is practicaly their job.
They will eat what fits in their mouth, whenever it is available, because in the wild they don't know when their next meal is coming.