How to Calculate Your BMI (Body Mass Index)
Learn to calculate your BMI and interpret the results. Understand categories, limitations, and usefulness of this index. Track your progress with Voical.
Calorie calculation examples by profile
Sedentary woman, 30 years old, 132 lbs, 5'5"
Active woman, 30 years old, 132 lbs, 5'5"
Sedentary man, 30 years old, 165 lbs, 5'10"
Active man, 30 years old, 165 lbs, 5'10"
What is BMI?
Body Mass Index (BMI) is a simple indicator that relates your weight to your height. Developed by Belgian statistician Adolphe Quetelet in the 19th century, it allows quick assessment of whether a person is underweight, normal weight, overweight, or obese. The formula is: BMI = weight (kg) / height (m)^2.
BMI categories
The WHO defines the following categories: BMI < 18.5 = underweight, BMI 18.5-24.9 = normal weight, BMI 25-29.9 = overweight, BMI 30-34.9 = obesity class I, BMI 35-39.9 = obesity class II, BMI >= 40 = obesity class III (morbid). These thresholds are the same for adult men and women.
Usefulness of BMI
BMI is useful as a quick screening tool at the population level. It helps identify people potentially at risk for weight-related health problems. It's a simple starting point that requires only two easily accessible measurements.
Important limitations of BMI
BMI doesn't distinguish fat mass from muscle mass. A muscular athlete may have a high BMI while being in excellent health. Conversely, an elderly person with little muscle may have a normal BMI but too much fat. BMI doesn't account for fat distribution (abdominal fat is more dangerous).
Important
Never go below 1200 kcal/day (women) or 1500 kcal/day (men) without medical supervision. Too aggressive a deficit can be dangerous for your health and counterproductive for weight loss.
Complete Guide to Calculating and Interpreting Your BMI
Body Mass Index is one of the most widely used health indicators in the world. Understanding how to calculate and interpret it helps you understand where your weight stands relative to health norms.
The BMI Formula
Basic Formula
BMI = Weight (kg) / Height (m)^2
Or in imperial units: BMI = (Weight (lbs) / Height (inches)^2) x 703
Calculation Examples
Example 1: Woman, 132 lbs (60 kg), 5’5” (1.65 m)
- BMI = 60 / (1.65 x 1.65)
- BMI = 60 / 2.7225
- BMI = 22.0 (Normal weight)
Example 2: Man, 187 lbs (85 kg), 5’10” (1.78 m)
- BMI = 85 / (1.78 x 1.78)
- BMI = 85 / 3.1684
- BMI = 26.8 (Overweight)
Example 3: Man, 209 lbs (95 kg), 5’11” (1.80 m)
- BMI = 95 / (1.80 x 1.80)
- BMI = 95 / 3.24
- BMI = 29.3 (Overweight, near obese)
BMI Interpretation Table
| BMI | Category | Health Risks |
|---|---|---|
| < 16 | Severe underweight | Very high |
| 16 - 16.9 | Moderate underweight | High |
| 17 - 18.4 | Underweight | Moderate |
| 18.5 - 24.9 | Normal weight | Low |
| 25 - 29.9 | Overweight | Moderate |
| 30 - 34.9 | Obesity class I | High |
| 35 - 39.9 | Obesity class II | Very high |
| >= 40 | Obesity class III | Extremely high |
Limitations of BMI
What BMI Doesn’t Measure
- Body composition: A bodybuilder with lots of muscle will have a high BMI without being unhealthy
- Fat distribution: Abdominal (visceral) fat is more dangerous than subcutaneous fat
- Age: Elderly people naturally lose muscle mass
- Sex in detail: Women naturally have more body fat than men
- Ethnicity: Risk thresholds vary across populations
Complementing BMI with Other Measures
For a more complete assessment:
- Waist circumference: > 37 inches (men) or > 31.5 inches (women) = increased risk
- Waist-to-hip ratio: > 0.90 (men) or > 0.85 (women) = high risk
- Body fat percentage: Measured by bioimpedance or skinfold calipers
From Diagnosis to Action
If your BMI indicates overweight or obesity, the first step is to calculate your actual caloric needs (TDEE) and create a moderate deficit of 500-700 kcal/day for healthy weight loss.
Track Your Progress with Voical
BMI is just a starting point. To reach and maintain a healthy weight, tracking your diet is essential. Voical simplifies this tracking by allowing you to photograph your meals for automatic calorie counting.