BMI categories for adults
These are the World Health Organization categories used for adults aged 18 and over. The same cut-offs apply to men and women.
| Category | BMI (kg/m²) |
|---|---|
| Underweight | below 18.5 |
| Healthy weight | 18.5 to 24.9 |
| Overweight | 25.0 to 29.9 |
| Obesity class I | 30.0 to 34.9 |
| Obesity class II | 35.0 to 39.9 |
| Obesity class III | 40.0 and above |
People of Asian descent tend to carry more body fat at a given BMI. A WHO expert consultation (2004) suggested treating 23 and 27.5 as points for public health action, and some countries use lower cut-offs than the table above. If this applies to you, ask your doctor which thresholds they use.
The formula
BMI = weight (kg) ÷ height (m)²In pounds and inches: BMI = 703 × weight (lb) ÷ height (in)². The calculator converts for you if you choose imperial units.
Healthy weight for a height is found by running the formula backwards: a BMI of 18.5 multiplied by height squared gives the lower end, and 24.9 multiplied by height squared gives the upper end.
Worked example
A person 172 cm tall who weighs 78 kg.
- Height in metres = 1.72, so height squared = 1.72 × 1.72 = 2.958
- BMI = 78 ÷ 2.958 = 26.4, which is in the overweight range (25.0 to 29.9)
- Healthy range for 172 cm = 18.5 × 2.958 to 24.9 × 2.958 = 54.7 to 73.7 kg
- The top of that range is 4.3 kg below the current weight
Healthy weight range by height
Use this table if you want a quick answer without the calculator.
| Height | Healthy range (kg) | Healthy range (lb) |
|---|---|---|
| 150 cm (4 ft 11 in) | 42 to 56 kg | 92 to 124 lb |
| 155 cm (5 ft 1 in) | 44 to 60 kg | 98 to 132 lb |
| 160 cm (5 ft 3 in) | 47 to 64 kg | 104 to 141 lb |
| 165 cm (5 ft 5 in) | 50 to 68 kg | 111 to 149 lb |
| 170 cm (5 ft 7 in) | 53 to 72 kg | 118 to 159 lb |
| 175 cm (5 ft 9 in) | 57 to 76 kg | 125 to 168 lb |
| 180 cm (5 ft 11 in) | 60 to 81 kg | 132 to 178 lb |
| 185 cm (6 ft 1 in) | 63 to 85 kg | 140 to 188 lb |
| 190 cm (6 ft 3 in) | 67 to 90 kg | 147 to 198 lb |
| 195 cm (6 ft 5 in) | 70 to 95 kg | 155 to 209 lb |
What BMI cannot see
BMI uses only height and weight, so it cannot tell muscle from fat or show where fat is stored. That leads to predictable mistakes:
- Muscular people read high. A rugby player or a lifter can land in the overweight range with very little excess fat.
- People with little muscle read low. An older adult can sit in the healthy range and still carry a lot of body fat. This is sometimes called normal-weight obesity.
- Fat distribution matters. Fat around the waist is linked with higher health risk than fat on the hips and thighs, and BMI cannot tell the difference.
A simple second check is your waist. Measure around your middle at the level of your navel, relaxed, after breathing out. A widely used rule of thumb is to keep your waist below half your height. A waist-to-height ratio above 0.5 is worth discussing with a doctor even if your BMI looks fine.
What to do with your result
If you are in the healthy range, there is nothing to fix. If you are above or below it, treat the number as a prompt for a conversation rather than a verdict. Blood pressure, blood sugar, cholesterol, fitness, sleep and family history tell a doctor far more than BMI does. If you decide to change your weight, the daily calorie calculator shows a target and the protein calculator helps you keep muscle while you do it.
These results are general estimates for healthy adults, not medical advice. See the disclaimer for who should check with a professional first.