Generally, item names can be anything, like "LogWood", "Piston", "whatever" or "hello". However, there are some rules that you have to follow and some rules that are recommended.
An item stack has two components: item name and stack size. When defining an item stack, the two should be separated by "*".
The order doesn't matter. You can put either stack size first or item name first.
You can also omit the stack size, in which case it will be set to 1.
Here are some examples: (The "*" displays like an "x" in Minecraft, but it is different!)
A recipe has three parts: result, ingredients and machine. The format is RESULT=INGREDIENT>MACHINE
RESULT is a single item stack representing the output of this recipe.
INGREDIENT is a list of item stacks, representing the input of this recipe. The item stacks are separated by "+". For example: Lever=Stick+Cobblestone
MACHINE is the machine that processes this recipe (in modded Minecraft.) You can omit this part and it will be set to "Craft" by default
Here are some examples:
Note that the calculator doesn't care if the recipe actually exists. All it does is what you told it to do!
Once a recipe is defined, you can calculate by simply entering the item stack of what you want to craft!
Examples:
Notice that you don't always craft the exact number. For example, you can't craft exactly 50 planks because that takes 12.5 logs. In these cases, the calculator will round up automatically and craft 52 planks!