When most people think about getting the perfect body and strong, sculpted muscles, they think about spending hours in the gym. Many people assume there is a direct correlation between the amount of time they spend in the gym and the definition they will see in their muscles.

To an extent, that’s correct. It’s tough to build muscle if you never exercise. But that theory ignores an important component of creating a muscular physique.

Strong bodies are made as much in the kitchen as they are in the gym.

You can spend all day lifting weights and doing cardio. However, if you have pounds of fat covering your muscles, it will be difficult for anyone to notice your strong core. If you’re interested in getting more definition in your muscles, you can start by looking at what and how much you’re eating.

Every box with nutritional information says the numbers are “based on a 2,000 calorie diet,” but is that how much you should be eating? Probably not. Without knowing you or knowing anything about your lifestyle, it’s impossible to know exactly how many calories you should be eating each day.

Thankfully, there are tools that can help you figure that out. The formula below will give you a good idea of how many calories you should be eating each day if you’re interested in maintaining your current weight. If you’re trying to add muscle mass or lose weight, you’ll want to adjust that total accordingly. Livestrong provides a good estimate of how you should alter your daily caloric intake to meet your goals.

Now, if you’re interested in knowing how many calories you should eat in a day to maintain your current weight, complete the following calculations.

NOTE: You don’t use each of the numbers right away, so it’s easiest if you draw nine lines and label them A through I. Then, you can easily pull the number from any line when it’s needed a few questions later.

• A.  Start with this number: 864 (men) or 387 (women)
• B.  Multiply your age by: 9.72 (men) or 7.31 (women)
• C.  Subtract line B from line A. The result may be negative, and that’s okay.
• D.  Multiply your weight in pounds by: 6.39 (men) or 4.91 (women)
• E.  Multiply your height in inches by: 12.77 (men) or 16.78 (women)
• F.  Add lines D and E
• G.  Enter the number corresponding with your daily physical activity level:
  1. Sedentary (no regular activity) 1
  2. Low activity (up to 30 minutes daily) 1.12 (men) or 1.14 (women)
  3. Active (30-60 minutes daily) 1.27
  4. Very active (more than 60 minutes) 1.54 (men) or 1.45 (women)
• H.  Multiply line F by line G.
• I.  Add lines C and H. This is your total daily caloric maintenance level.

If (like my husband) you’re too lazy to do all those calculations: There are several places online where you can insert a few basic details, and a computer program will do the math for you. I tested about a dozen of these programs, and most came within 500 calories of calculation above. Remember, if you want an accurate calculation, it’s important to use as much information as you have available. For that reason, I would use the formula above.

Otherwise, try this calculator at Livestrong. It’s very close to the calculation above, and it also gives you the option to see how many calories you should eat if you’re interested in losing or gaining weight.

Source: Personal Nutrition, “Energy Needs,” Marie A. Boyle and Sara Long, Wadsworth Cengage Learning, 2010