Flaked and powdered agar agar need to be used in different proportions, unfortunately many recipes do not specify which is being called for, but here are a few guidelines:
Powdered agar agar can be substituted for the same quantity of powdered gelatine in a recipe.
For every teaspoon of agar agar powder, you should substitute a tablespoon of agar agar flakes.
For a firm jelly you require approximately 2 teaspoons of powder or 2 tablespoons of flakes per 1 pint / 600ml of liquid.
Agar agar should be soaked in the liquid first for 10-15 minutes, then gently brought to the boil and simmered while stirring until it dissolves completely, this will take about 5 minutes for powder and 10-15 minutes for flakes. Unlike gelatine, agar agar can be boiled and can even be re-melted if necessary. If you are unsure as to the setting ability of your gel, test a small amount on a cold saucer - it should set in 20-30 seconds, if not you may need more agar agar, if too firm - add some more liquid.
To jell about 2 c. of liquid:
1 T. animal gelatin = 2 T. agar flakes =1 tsp. agar powder
(Since specifying the suitable amount of agar-agar needed in a certain recipe depends on the type of agar-agar product used and its gelling properties, it is best to follow the measuring and cooking instructions on the agar-agar package)