How To Use a BMI Calculator
If you have put a lot of time and effort into your workout or weight loss program, it makes sense to set goals and track your progress. BMI calculators can help you achieve this by simply keying in a few inputs. However, some BMI calculators are more technical and a bit difficult to use. We take a closer look at how to use a BMI calculator to help you better understand and acheive your health goals.
What Is a BMI Calculator?
A BMI calculator is a tool that calculates the measure of body fat by computing your Body Mass Index, which results from dividing your weight by the square of your height.
Since obesity is an ongoing public health challenge, it is necessary to keep track of body fat levels for healthy living.
Other methods of measuring fat levels in the body, like DXA, isotope dilution, bioelectrical, and impedance are expensive and require trained personnel. However, using a BMI calculator is easy and affordable, making it one of the best alternatives for the masses.
What Are the Different Sections of a BMI Calculator?
The key to learning how to use a BMI calculator is understanding the different sections. A basic BMI calculator has a section for selecting between imperial or metric inputs. Once selected, you can insert your height (in feet and inches) and weight (in pounds), or the same in meters/centimeters and kilograms, respectively, then calculate your BMI. Compare the result with these categories to determine your weight.
- Less than 18.5 = underweight
- 18.5 – 24.9 = normal/healthy weight
- 25 – 29.9 = overweight
- 30 and above = obese
However, the basic calculator is not ideal for certain people like bodybuilders and athletes because it fails to consider if the weight is muscle or fat. Also, children (who are still growing) and the elderly (who are shedding muscle mass) might have a lower BMI due to their age.
BMI calculators take care of these variables because they have inputs for gender, age, activity, and other factors. Additionally, they have these key sections:
Basal Metabolic Rate
BMR is the amount of energy required by your body in a day if you remain motionless. Various formulas exist to calculate this rate, but Mifflin-St Jeor is more accurate if you don’t remember your body fat percentage. However, if you know this percentage, the Katch-McArdle formula is the most accurate. You can also select the average BMR, use a multiplier of weight, or custom input.
Total Daily Energy Expenditure
TDEE is a measure of the number of calories you burn in a day. The section gives you three options, which are:
- Simple multiplier (of weight)
How To Use a BMI Calculator for Weight Loss
Weight loss is often more successful when someone sets goals. Some of the required inputs for setting the weight loss targets include:
- Goal weight, which should be lower than your current weight
- Activity (sedentary to highly-active)
- Workouts per week
- Your goal in terms of weight loss speed
With all these variables, the calculator delivers multiple results. First, it shows you your weight class, which is either: underweight, healthy weight, overweight or obese.
Depending on your current weight and final expected weight, the tool indicates how long it will take to achieve the results. You also get the following outputs:
- Maximum Fat Metabolism (MFM): number of calories you can consume below your TDEE without losing muscle mass
- Maximum Recommended Daily Calories: TDEE – MFM
- Workout Calories: Equivalent to TDEE
- Rest calories
These results can help guide your calorie intake, which should work hand-in-hand with your workout plan to ensure you achieve your weight loss goal.
Macronutrients are foods that provide energy/calories in large quantities to help maintain bodily functions. They include three broad classes: carbohydrates, proteins, and fats. The quantities/balancing of these nutrients in diets is vital to delivering the right amount of energy required by the body. They should be:
- Carbohydrates: 45 – 65%
- Protein: 10 – 35%
- Fat: 20 – 35%
The variation in nutrient balance (percentages) is due to different requirements in energy intake. For instance, athletes and bodybuilders need a high-calorie intake, and the workout intensity determines the calorie requirement.
If you participate in a general fitness program (30 – 40 minutes per day, three times per week), you need macronutrients balanced in these levels:
- Carbohydrates: 45 – 55% (3 – 5 grams per kilo of body weight per day)
- Protein: 10 – 15% (0.8 – 1 gram per kilo of body weight per day)
- Fat: 25 – 35% (0.5 – 1.5 grams per kilo of body weight per day)
However, if you are in a moderate fitness program (2 – 3 hours per day, 5 – 6 times per week), you need a slightly different nutrient balance.
- Carbohydrates (55 – 65%) or 5 – 8 grams per kilo of body weight per day
- Protein (20 – 30%) or 1 – 1.5 grams per kilo of body weight per day
- Fat (up to 30%) or 0.5 – 1 gram per kilo of body weight per day
For weight loss programs, balance the macronutrients using these percentages:
- Carbohydrates (45 – 50%) or 3 – 4 grams per kilo of body weight per day
- Protein (25 – 30%) or 1.5 – 2 grams per kilo of body weight per day
- Fat (20 – 25%) or 0.3 – 0.5 grams per kilo of body weight per day
How To Create a Meal Schedule Based on Macro Nutrients and BMI Calculator Numbers
With the results from your BMI calculator, you can use the Maximum Recommended Daily Calories (MRDC) or Workout Calories (WC) to calculate the required macronutrients. Begin by splitting the MRDC or WC using the respective nutrient percentages of your workout/weight loss program. Next, convert these nutrient calories into grams using these formulas:
- 1 gram of carbohydrates = 4 calories
- 1 gram of proteins = 4 calories
- 1 gram of fats = 9 calories
Once you have determined the food quantity/weight, measure the respective nutrients to create your meal schedule for each day of your program.
For instance, if your calculation shows that you need 1000 calories for weight loss purposes, you can pick 45% carbohydrates, 30% protein, and 25% fat (total should be 100). With these ratios, the nutrients split into 450, 300, and 250 calories, respectively.
Converted to grams, you should consume 112.5 grams of carbohydrates, 75 grams of proteins, and 27.78 grams of fat per day.