Hello, ive searched alot without success finding the correct basket weight for both the single, double and bottomless portafilter. Some threads people speak about their experience, some prefer 17g while other 19,
But is there any official "correct" basket size info anywhere?

How to Adjust Dose and Grind Setting by Taste is a good place to start.

Yes ive read it, very nice and informative! But isnt there any official answer how many grams in the portafilter the manufacturer has labeled it? Or is this just from the kinda "beginner" or auto machine that just do this in the manual, example the breville dual boiler i know has it in the manual. So expensive pro machine dosent mention any correct size, they reckon the barista is good enough too find it by themself?

I've owned three Rocket Espresso machines, and I do not recall there being an official dose size. You determine the dose based on your desired result, and the machine works well with whatever you choose.

Rocky

I've found that dosing evenly and without compression followed by a clean level strike off yields a reasonable starting point for any double basket. I've always assumed this was by design. Weighing is a great idea for consistency, but I would not expect that for a busy pro barista.

But surely the basket must have been designed to support a certain volume/weight? i mean different basket varies in weight, some double dose are about 18g and some are 14g. And i thought coffee shops pre programmed their grinder to about that 18g dose, or whatever they need so they get consistency every time.

Im also friends with some baristas, just people working at cafes, and they didnt really have expertise in making coffee, they only had taken some classes. so when the term pro barista is mentioned, do they they mean special coffee expert with alot of experience, research and practice, or just a regular cafe employee with espresso machine?

Why not contact the manufacturer, importer or retailer? We pay a lot of money for these machines. Someone in the supply chain should be able to give you the correct answer if there is one. Good luck.

Rocket includes the dose amount in their booklet that comes with every machine. 14 gram for double and 7 gram single. The bottomless comes with a triple basket which is 21 gram. Obviously it varies with grind size and yield so just go by what best suits your taste. Coffee expands when extracting so don't go by what it looks like in the basket. For better results use precision baskets like VST.

I have an R58 and use 15 grams in the rocket double basket and 18 grams in a 18 gram VST basket. Wife prefers her latte with less strength than me. I don't use triple basket as my lattes are only 6oz. Still waiting on my 15 gram VST to arrive.