how do I measure fish food to ensure my fish gets the right amount not to much or to little?

the 2-3 minute feeding rule is for community tanks only. What kind of fish do you have? This is what will determine how much to feed him.

If you only have one or two fish then only feed them what they can eat in 45 seconds to a minute. Once or twice a day depending on the species.

For larger fish, weigh them on a scale (WITH WATER! you can look up how to do this on youtube!). They should be eating 20-30% of their body weight on a daily basis.

if you have a betta fish, then 1-2 pellets a day will be perfectly fine. A betta's stomach is only as large as its eye and too much food can cause major problems.

You can't measure fish food buy you can look at the time and see how much food your fish consume in 2-3 minutes after 2-3 minutes they're no longer hungry but their instincts are to consume whatever the can since in nature they might not get a meal for a couple weeks.

Usually people feed too much, since you'd have to not feed for weeks to cause any harm to the fish.

So, without any useful info in your question I can assume you overfeed,

and you shouldn't overfeed. The instructions on the food are pure nonsense and recommend feeding 5 to 10 times too much. So don't do that.

Edit: @anon, said this " how much food your fish consume in 2-3 minutes" and I would add to that;

how much food your fish consume in 2-3 minutes, or less, with none left in the tank, none floating, none on the gravel, none anywhere.