How to check your BMI
- Pick your units. Choose US (pounds, feet and inches) or metric (kilograms and centimeters).
- Enter your height and weight. Weigh yourself in the morning in light clothes for the most consistent reading.
- Tick the Asian cut offs if they apply. Health bodies in many Asian countries use lower thresholds, 23 for overweight and 27.5 for obesity.
- Read your result. See your BMI, your category and the healthy weight range for your height.
How BMI is calculated
Body mass index is your weight in kilograms divided by your height in meters squared. For someone who weighs 70 kg and is 1.75 m tall, that is 70 divided by 3.06, a BMI of about 22.9. In pounds and inches, multiply weight in pounds by 703 and divide by height in inches squared.
BMI categories for adults
| BMI | WHO category | Asian cut offs |
|---|---|---|
| Below 18.5 | Underweight | Below 18.5 |
| 18.5 to 24.9 | Healthy weight | 18.5 to 22.9 |
| 25 to 29.9 | Overweight | 23 to 27.4 |
| 30 to 34.9 | Obesity class 1 | 27.5 and above |
| 35 to 39.9 | Obesity class 2 | |
| 40 and above | Obesity class 3 |
The World Health Organization suggests lower cut offs for people of Asian heritage, because health risks such as type 2 diabetes tend to rise at a lower BMI. Tick the box in the calculator to use them.
BMI chart: healthy weight for your height
Each row is a real run of the calculator. The range is the weight that gives a BMI of 18.5 to 24.9 at that height, for women and men alike.
| Height | Healthy weight (lb) | Height (cm) | Healthy weight (kg) |
|---|---|---|---|
| 4 ft 10 in | 89 to 119 lb | 147 cm | 40.0 to 53.8 kg |
| 5 ft 0 in | 95 to 127 lb | 152 cm | 42.7 to 57.5 kg |
| 5 ft 2 in | 101 to 136 lb | 157 cm | 45.6 to 61.4 kg |
| 5 ft 3 in | 104 to 141 lb | 160 cm | 47.4 to 63.7 kg |
| 5 ft 4 in | 108 to 145 lb | 163 cm | 49.2 to 66.2 kg |
| 5 ft 5 in | 111 to 150 lb | 165 cm | 50.4 to 67.8 kg |
| 5 ft 6 in | 115 to 154 lb | 168 cm | 52.2 to 70.3 kg |
| 5 ft 7 in | 118 to 159 lb | 170 cm | 53.5 to 72.0 kg |
| 5 ft 8 in | 122 to 164 lb | 173 cm | 55.4 to 74.5 kg |
| 5 ft 10 in | 129 to 174 lb | 178 cm | 58.6 to 78.9 kg |
| 6 ft 0 in | 136 to 184 lb | 183 cm | 62.0 to 83.4 kg |
| 6 ft 2 in | 144 to 194 lb | 188 cm | 65.4 to 88.0 kg |
| 6 ft 4 in | 152 to 205 lb | 193 cm | 68.9 to 92.8 kg |
Weight is rounded to the nearest pound, so a weight right at the top of a range can read 25.0 in the calculator.
BMI for women: by height and by age
Women use the same formula and the same categories as men. What changes the answer is height: a 5 ft 4 in woman has a healthy range of 108 to 145 lb, and a 5 ft 7 in woman 118 to 159 lb. At 160 lb, the calculator gives 27.5 at 5 ft 4 in and 25.1 at 5 ft 7 in, both just into overweight.
Age does not change the adult categories, but it changes how much the number means. Over 60 and over 70, people tend to lose muscle, so the same BMI can hide more fat. A 2014 review of older adults in the American Journal of Clinical Nutrition found the lowest risk of death at a BMI around 27, and higher risk below about 23. For an older woman, a BMI a little over 25 is usually less of a worry than one under 23, and waist size and strength matter more. Under 18, BMI is judged against growth charts for age and sex, so the calculator does not give a category.
Metric example: 165 cm and 70 kg
A real run in metric: 70 ÷ (1.65 x 1.65) = 70 ÷ 2.72 = a BMI of 25.7, overweight. The healthy range at 165 cm is 50.4 to 67.8 kg, so the gap is 2.2 kg. At 178 cm and 85 kg the BMI is 26.8, and the healthy range tops out at 78.9 kg, a gap of 6.1 kg.
What BMI can and can't tell you
BMI is a quick, free screening tool that works well across large groups of people, which is why doctors and health agencies use it. But it has real limits for individuals. It doesn't separate muscle from fat, so athletes can score as overweight. It doesn't show where fat sits, and fat around the waist carries more risk than fat on the hips. It is also less reliable for older adults, who may have less muscle at the same BMI.
Worked example: 5 ft 6 in and 165 lb
Here is a real run of the calculator for someone who is 5 ft 6 in (1.676 m) and weighs 165 lb (74.8 kg).
| Step | Working | Result |
|---|---|---|
| Height squared | 1.676 x 1.676 | 2.81 m² |
| BMI | 74.8 ÷ 2.81 | 26.6, overweight |
| Healthy range for this height | BMI 18.5 to 24.9 | 115 lb to 154 lb |
| To reach the range | 165 − 154 | 11 lb |
In pounds the shortcut is weight in lb x 703 ÷ height in inches squared: 165 x 703 ÷ (66 x 66) = 26.6, the same answer.
What to do with your result
If your BMI is outside the healthy range, it's a prompt to look closer rather than a verdict. Talk to a doctor, and use the calorie calculator and weight loss calculator to plan realistic, gradual changes. The ideal weight calculator compares several formulas for your height.
Sources: World Health Organization BMI classification; WHO Expert Consultation on BMI in Asian populations, The Lancet 2004; NHS and CDC adult BMI guidance.
