Typically it is figured as a cost percentage ratio. Choosing what cost ratio to use is very important. Higher labor items should typically have a larger multiplier of the cost to make up for the increased labor.
I am not going to go into how to do this, but I will simply say that most accountants who are experienced in the restaurant industry like tgo see a combined food/labor cost no higher then 55%
So if your food-cost is 30%, your labor cost needs to be at 25% or less for them to be pleased (meaning you making a profit)
Typically most projected food cost ratios will bee between 25-30% a food cost ratio of 40% or higher is mostly used for "Not For Profit" operations such as a members only country club