BMI Calculator
Calculate your Body Mass Index instantly. Free BMI calculator with metric and imperial units, category and your healthy weight range. Private — runs in your browser.
Your Body Mass Index (BMI) is a quick screening number that relates your weight to your height. It's used worldwide by health organisations to flag whether an adult's weight may pose a health risk. This free calculator gives you your BMI, tells you which category you fall in, and shows the healthy weight range for your height so you have a concrete target.
BMI is a useful starting point, but it has limits — it can't tell muscle from fat. A lean, muscular athlete can read "overweight" while carrying very little body fat. Use BMI as one signal alongside waist measurement, how your clothes fit, and how you feel. For body composition specifically, try our body fat calculator.
Calculate your BMI
BMI categories explained
| BMI | Category | What it suggests |
|---|---|---|
| Below 18.5 | Underweight | May indicate under-nutrition; worth a check-up. |
| 18.5 – 24.9 | Healthy weight | Associated with the lowest health risk for most adults. |
| 25.0 – 29.9 | Overweight | Slightly raised risk; lifestyle changes can help. |
| 30.0 and above | Obesity | Higher risk of metabolic and cardiovascular conditions. |
Why BMI isn't the whole story
BMI was designed to track populations, not to judge individuals. Because it only uses height and weight, it overestimates fat in muscular people and can underestimate it in older adults who've lost muscle. It also doesn't account for where you carry fat — abdominal (visceral) fat around the organs is more strongly linked to health risk than fat on the hips.
Combine BMI with a waist measurement. For many adults, a waist over roughly 94 cm (37 in) for men or 80 cm (31.5 in) for women signals raised risk regardless of BMI. Then track your body fat percentage over time — that's what actually changes when you train.
What to do with your number
If your BMI suggests you'd benefit from losing fat, the path is simple and proven: a modest calorie deficit plus resistance training to keep your muscle. Start with our how to lose fat guide and calculate your calorie needs with the TDEE calculator. If you're underweight or want to add muscle, see how to build muscle.
Sources & further reading
- World Health Organization — Obesity and overweight: Body mass index.
- Centers for Disease Control and Prevention (CDC) — About Adult BMI.
- NHS — BMI healthy weight categories.
External links are provided for reference and do not imply endorsement. arsenal.fit is an independent publisher and is not affiliated with any cited organisation.