Use this BMI calculator to estimate body mass index based on height and weight.
BMI, or body mass index, is a general screening measurement that compares weight to height. It can be useful for understanding broad weight categories, but it does not measure body fat directly and does not diagnose health.
BMI is a screening indicator and does not measure body fat directly. It can misclassify athletes, the elderly, and pregnant women. For personalized health advice, consult a qualified medical professional.
How BMI is calculated
Body Mass Index is a single number that relates your weight to your height. The same number can be reached from metric or imperial measurements — the calculator above converts imperial figures to metric internally, so both routes give the same result.
The height term is squared, which is the part most people miss. Because the bottom of the fraction grows with the square of your height, BMI rises steeply as weight goes up but only gradually as height goes up. That squaring is also why BMI tends to read high for very muscular or very tall people and low for very short people — the formula assumes body mass scales with height squared, which is an approximation, not a biological law.
Worked examples
- Convert height to meters: 170 cm ÷ 100 = 1.70 m
- Square the height: 1.70 × 1.70 = 2.89
- Divide weight by that: 70 ÷ 2.89 = 24.2
BMI 24.2 → Normal weight. A healthy weight for this height runs about 53.5–72.0 kg.
- Convert height to inches: (5 × 12) + 9 = 69 in
- Square the height: 69 × 69 = 4,761
- Multiply weight by 703: 703 × 160 = 112,480
- Divide: 112,480 ÷ 4,761 = 23.6
BMI 23.6 → Normal weight.
BMI categories for adults
These ranges come from the World Health Organization and apply to most adults aged 20 and over, regardless of sex. They are screening bands, not diagnoses.
| BMI range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obesity |
Obesity is sometimes further split into 3 categories: 30.0–34.9 (class I), 35.0–39.9 (class II), and 40.0 or more (class III). Some health authorities also flag a lower threshold of 23 as a point of raised risk for people of South Asian, Chinese, and some other Asian backgrounds, because health risks can appear at a lower BMI in these groups.
Healthy weight range by height
The “normal” band (BMI 18.5–24.9) translates into a different weight range at every height. The table below shows the approximate healthy span for a selection of heights, in both unit systems.
| Height | Healthy weight (kg) | Healthy weight (lb) |
|---|---|---|
| 5 ft 0 in (152 cm) | 43 – 58 kg | 94 – 127 lb |
| 5 ft 3 in (160 cm) | 47 – 64 kg | 104 – 141 lb |
| 5 ft 6 in (168 cm) | 52 – 70 kg | 115 – 155 lb |
| 5 ft 9 in (175 cm) | 57 – 76 kg | 125 – 168 lb |
| 6 ft 0 in (183 cm) | 62 – 83 kg | 137 – 184 lb |
| 6 ft 3 in (191 cm) | 67 – 91 kg | 149 – 200 lb |
Figures are rounded. Use the calculator above for a number tailored to your exact height and weight.
Where BMI falls short
BMI is popular because it needs only two easy measurements and no equipment. That simplicity is also its weakness: it counts total weight without knowing what that weight is made of.
- Muscle reads as risk. Athletes and people who lift weights often land in the “overweight” or “obese” bands despite low body fat, because muscle is dense and heavy.
- It misses where fat sits. Two people with the same BMI can carry fat very differently. Fat around the abdomen carries more health risk than fat on the hips and thighs, and BMI cannot tell them apart. Waist circumference is often used alongside it.
- Age changes the picture. Older adults tend to lose muscle and gain fat, so a “normal” BMI can hide a higher body-fat percentage later in life.
- It is not for everyone. BMI is not valid for children and teens (who use age- and sex-specific percentile charts), for pregnant people, or as a standalone diagnosis for anyone.
Treat your BMI as a starting prompt for a conversation, not a verdict. If your number sits outside the normal band, it is a reason to look closer — with a clinician, and with measures like waist size, blood pressure, and activity level — not a diagnosis on its own.
Frequently asked questions
What is a healthy BMI?
For most adults, a BMI between 18.5 and 24.9 is considered a healthy weight. Below 18.5 is underweight and 25 or above is overweight. These bands are screening guides — a value just outside the range is not automatically a health problem, and a value within it does not guarantee good health.
Is BMI accurate?
BMI is an accurate calculation but a rough indicator. The arithmetic is exact, yet the number only estimates body fatness for a population — it can misjudge any single person, especially someone very muscular, very tall or short, older, or from a group with different body-composition norms. It works best as a quick first screen, not a precise measure of health.
Does BMI differ for men and women?
The formula and the adult category ranges are the same for men and women. On average, women carry a higher proportion of body fat than men at the same BMI, so the single number hides a real difference in body composition — another reason to read BMI alongside other measures rather than on its own.
What is the difference between BMI and body fat percentage?
BMI uses only height and weight, so it estimates body composition indirectly. Body fat percentage measures the actual share of your weight that is fat, usually with calipers, a smart scale, or a body scan. Body fat percentage is more informative but harder to measure reliably at home; BMI is less precise but takes two seconds.
Can I use this BMI calculator for my child?
No. For anyone under 20, BMI is interpreted against age- and sex-specific percentile charts rather than the fixed adult ranges, because healthy body composition changes rapidly during growth. Ask a pediatrician or use a dedicated child-and-teen BMI percentile tool instead.
Why does my BMI say overweight when I feel fit?
This is the most common complaint about BMI, and usually it is the formula’s limitation rather than your fitness. Muscle weighs more than fat for the same volume, so a lean, strong body can push BMI into the overweight band. If you train regularly and carry visible muscle, a body fat or waist measurement will give you a fairer read.
Disclaimer
This BMI calculator is for general informational purposes only and is not medical advice. It does not diagnose health conditions. Consult a qualified healthcare professional for personal medical guidance.