STEP-1 :

Choose one of the dimension criteria from the given topmost list.

STEP-2 :

Enter the value for the above selected dimension and choose unit for the same from the given list (near the value to be input).

STEP-3 :

Click on Add button to make your value selection permanent and it will be shown in a list below.

At any point of time double-click on the permanent selection to remove it.Also you can use it for replacing the value.

STEP-4 :

When you are done with your selection, hit Calculate button for result.

Hit Reset button at any point to reset all your selected values.