You have to figure an average per meal for both the sales and the costs - so in your example you might decide that your average food cost is 37.5% of sales.

You could also break it down by time of day - i.e. lunch vs. dinner. That's how people figure out whether it makes sense to do both if they are currently only serving one of those.

OK! i'm little confused! I know I should have the fixed costs and variable costs and put it in some formula! my question is about food cost. where you should consider the food cost on your break even point analysis? Since the food cost is directly related to your sale, how you consider it to calculate break even point? For example, maybe on March, you sell 10,000 and your food cost is 3500 and in another month, you sell 20,000 and your food cost is around 8000. Since the food cost is so variable and depend on your sale, how you can consider it for calculation of break even point?