When using a powdered form, the general rule of thumb is to use 1 teaspoon for every cup (8.45 fl oz / 250ml) of liquid you need to thicken. This ratio will also vary depending on how thick you want the liquid to be.
An agar gel has a thick consistency somewhere between a runny sauce and sets jelly. For this consistency, we use 1 teaspoon (5 grams) of agar powder and 2 cups (500 ml) of liquid. This liquid can be anything you’d like.
Gelatin is a great substitute for agar and has similar properties. Gelatin doesn’t have to be boiled since it has a lower melting point, but that also means that it won’t withstand high heat. Gelatin is also not suitable for vegetarians or vegans since it is made from animal products.