How much powder to use? Usucha & Koicha
In general, you can often find instructions on how much powder to use for a specific amount of matcha powder on the container of the product you bought.
It's usually 2g of sieved powder for one cup (a tea bowl). 5-10ml of hot but not boiling water is used to whisk and blend the clumps, and then the rest of the water is poured in. You can enjoy it pure, or some add (plant) milk into this cup. Some also use about 60ml or so of the finished matcha to pour into a desired amount of (plant) milk separately. You can vary these depending on how strong and creamy you want things to be. These are the base guidelines most products have, and this results in usucha, thin tea, which is the most popular form to consume - it's what I make for my reviews, but I eyeball the amount of powder because my food scale doesn't accurately measure that low.
You sometimes also see really thick, creamy matcha in bowls. It looks like melted ice cream. That's koicha.
This uses double the amount of sieved powder, so usually 4g (or more) and only very little hot water; around 10-15ml. This is usually only done with really high grade matcha that has very little bitterness and a lot of umami and sweetness; otherwise, if you make this with lower grade, more bitter matcha, it would be way too bitter. It is said that matcha with "mukashiοΌζοΌ" in its name is for Koicha, and matcha with "shiroοΌη½οΌ" is for Usucha, but I have not encountered this yet in the products available to me in the West.
This is also not how you commonly drink it daily, but for special guests and tea ceremonies. Feel free to try it sometimes for special occasions, but be careful to select the correct kind of matcha and be mindful of the caffeine content. If it ends up too strong for your taste, don't throw it away! Use it as a base for your usual usucha matcha, or add water and (plant) milk.
Here you can see me showcase some koicha:
Technically, usucha and koicha also have differences in chasen (the whisk), bowls and more, but this post is not about the ceremonies, just for you consumption :)