1. Enter height and weight
Use centimeters and kilograms, or switch to feet/inches and pounds — the calculator converts everything for you.
Free online tool
BMI calculator with healthy weight range.
Enter your height and weight in metric or imperial units and get your body mass index, the WHO category it falls in, and the healthy weight range for your height — instantly, in the browser. Numbers are a starting point; daily movement is what changes them, and StepDay keeps your step, workout, and sleep trends honest.
How to use it
How to use the BMI calculator.
Two inputs, three answers: your BMI, your category, and your healthy range.
2. Read your BMI and category
Your BMI appears with the WHO adult category it falls in, from underweight to obesity class III.
3. Check your healthy range
The tool also shows the weight range that corresponds to a BMI of 18.5–24.9 for your height, so you have a concrete reference point.
Reference
The numbers behind the tool.
Formulas, reference tables, and practical guidance you can come back to.
WHO BMI categories for adults
The World Health Organization groups adult BMI into the ranges below. They apply to adults 20 and older, of any sex.
| BMI (kg/m²) | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obesity class I |
| 35.0 – 39.9 | Obesity class II |
| 40.0 and above | Obesity class III |
What BMI can and cannot tell you
BMI is a screening tool, not a diagnosis. It correlates with body fat across large populations, which makes it useful for spotting risk trends — but it says nothing about where fat sits (visceral fat matters most), how much muscle you carry, or your fitness level.
Two practical companions: waist circumference (risk rises above 94 cm / 37 in for men, 80 cm / 31.5 in for women) and your activity trend — someone walking 8,000+ steps a day at BMI 27 is in a very different position from someone sedentary at the same number.
Healthy weight range formula
The healthy range shown by this calculator is simply the BMI formula run backwards: healthy weight = 18.5 × height² to 24.9 × height² (height in meters). At 1.70 m that's 53.5–72.0 kg; at 5'10" (1.78 m) it's 58.6–78.9 kg.
FAQ
Frequently asked questions.
Quick answers about this tool and how to train with it.
How is BMI calculated?
BMI = weight in kilograms divided by height in meters squared (kg/m²). For example, 70 kg at 1.75 m is 70 ÷ (1.75 × 1.75) = 22.9. The same formula applies to men and women.
Is BMI accurate for muscular people?
Not very. BMI can't tell muscle from fat, so lean, muscular people often read as "overweight" while carrying little fat. Treat BMI as a population-level screening number, and combine it with waist measurement, body-fat estimates, and how your training is going.
What is a healthy BMI for adults?
The WHO defines the normal range for adults as 18.5–24.9. Some Asian populations use lower action points (23 for elevated risk, 27.5 for high risk), because health risks rise at lower BMI values in these groups.
Does BMI apply to children and older adults?
Children and teens need age- and sex-specific BMI percentiles, not the adult cutoffs — use a pediatric chart. In adults over 65, slightly higher BMI values are often not associated with worse outcomes, so interpret with more care.
For site owners
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