How to calculate BMI: formulas and steps
Body Mass Index (BMI) is an internationally recognized screening metric used by physicians, researchers, and public health organizations to evaluate body weight relative to stature.
1. Imperial BMI formula (US standard)
Step-by-step imperial calculation:
- Convert height to total inches (e.g. 5 feet 10 inches = 5 × 12 + 10 = 70 inches).
- Square your height (70 × 70 = 4,900).
- Multiply your weight by the conversion constant 703 (160 × 703 = 112,480).
- Divide the weight total by the squared height (112,480 ÷ 4,900 = 22.95 → rounds to 23.0).
2. Metric BMI formula (international standard)
For an individual weighing 72.5 kg with a height of 178 cm (1.78 m): BMI = 72.5 ÷ (1.78 × 1.78) = 22.88.
WHO adult BMI classification chart
| Weight Classification | BMI Range (kg/m²) | 5'10" (70 in) Weight Range | Associated Health Risk |
|---|---|---|---|
| Underweight | < 18.5 | Under 129 lbs | Malnutrition, immune compromise, osteoporosis |
| Normal Weight | 18.5 – 24.9 | 129 – 174 lbs | Lowest statistical mortality & cardiovascular risk |
| Overweight | 25.0 – 29.9 | 175 – 208 lbs | Moderate risk of high blood pressure and type 2 diabetes |
| Obesity Class I | 30.0 – 34.9 | 209 – 243 lbs | High risk of cardiovascular disease & joint stress |
| Obesity Class II | 35.0 – 39.9 | 244 – 278 lbs | Very high risk of chronic conditions |
| Obesity Class III | ≥ 40.0 | 279+ lbs | Extremely high health risk (severe obesity) |
Important clinical limitations of BMI
While BMI is an excellent broad epidemiological screening tool, it has notable limitations for individuals:
- Muscle Density: Muscle tissue is much denser than adipose body fat. Athletes, bodybuilders, and fitness enthusiasts frequently test in the "overweight" or "obese" range despite having very low body fat percentages.
- Age and Sarcopenia: Older adults naturally lose lean muscle mass. An elderly individual may test with a "normal" BMI while carrying excess visceral abdominal fat.
- Body Fat Distribution: BMI does not measure where fat is stored. Visceral fat stored around internal abdominal organs poses significantly greater cardiovascular and metabolic risk than subcutaneous fat stored around the hips and thighs.
Frequently asked questions about calculating BMI
What is a good BMI for a man vs. a woman?
Standard clinical BMI ranges established by the WHO apply equally to adult men and adult women. Both sexes have an optimal healthy range between 18.5 and 24.9, although women naturally carry roughly 6% to 11% more essential body fat than men at the same BMI.
How many pounds do I need to lose to reach a normal BMI?
Find the upper normal weight threshold for your height (BMI 24.9). For example, at 5'10", the upper normal limit is 174 lbs. If you currently weigh 195 lbs, losing 21 lbs brings you into the normal BMI category.
What other body composition metrics should I check?
Medical professionals frequently pair BMI with waist-to-hip ratio (WHR) and waist circumference (healthy target is under 40 inches for men and under 35 inches for women) to evaluate visceral fat accumulation.
Created and calculation-tested by Velour Trends · Updated 9 November 2026. Standard WHO/CDC biometric formulas verified. Report a calculation issue.