Overview
What this tool does
BMI (Body Mass Index) is weight divided by height squared. It's the standard population-level screening number doctors, insurers, and public-health agencies use to flag potential weight risks. This calculator handles both metric (cm + kg) and imperial (ft/in + lb), shows the WHO category your number falls into, and tells you the healthy weight range for your height. It also makes the limitations clear: BMI doesn't know muscle from fat, so weight-trained individuals frequently land in the "overweight" bracket while being perfectly healthy. Runs entirely in your browser, no signup.
How to
Use it in 3 steps
- Pick a unit system (metric or imperial).
- Enter your height and weight. The result updates live.
- Read the BMI number and its WHO category (Underweight / Normal / Overweight / Obese).
- Compare against the colored scale to see where you fall and how far you are from the next bracket.
- Reference the healthy weight range at the bottom for the kg or lb numbers that correspond to a BMI of 18.5-24.9 at your height.
FAQ
Frequently asked questions
▶What BMI is 'healthy'?
The WHO defines 18.5 to 24.9 as the healthy range. Below 18.5 is underweight, 25 to 29.9 is overweight, 30+ is obese. These thresholds are statistical correlations with health-outcome data at a population level, not personalised medical advice.
▶Why does BMI fail for muscular people?
BMI uses total weight without distinguishing fat mass from muscle mass. Muscle is denser than fat, so a very athletic person carrying a lot of muscle will score higher than a sedentary person of the same height carrying mostly fat, even though the athlete is healthier. For more accurate body-composition assessment, look at body-fat percentage measurements (DEXA scan, calipers, BIA).
▶Is BMI used differently for children or older adults?
Yes. For children, BMI is interpreted relative to age-and-sex percentile charts, not raw thresholds. For adults over 65, slightly higher BMI (up to ~27) is sometimes associated with better outcomes due to muscle-mass loss. This calculator uses the standard adult thresholds; consult a doctor for personalised interpretation.
▶Is my data sent anywhere?
No. The math runs in your browser. The height and weight you enter never leave your device.
▶Should I use BMI to decide if I need to lose weight?
BMI alone is a starting point, not a verdict. Combine it with how you feel, your fitness, family history, lab results (cholesterol, blood pressure, A1C), and a doctor's input. Don't crash-diet because a single number landed in a yellow bracket.