BMI Calculator — Body Mass Index

Enter your height and weight in your preferred unit system. The BMI value, WHO category and healthy weight range update live.

What is BMI?

BMI (Body Mass Index) is a single number that estimates whether your weight is in the typical range for your height. It is computed as weight in kilograms divided by height in metres squared (kg/m²); the imperial form multiplies pounds over inches squared by 703.

BMI is widely used because it's cheap to compute and reasonably correlates with body-fat percentage at the population level. It does not measure body composition directly — a muscular athlete and a sedentary person of the same height and weight share the same BMI but very different body fat. Use BMI as a starting point, not a diagnosis.

How to use this tool

Pick the unit system you prefer (metric or imperial) using the toggle at the top.
Drag the height and weight sliders, or type exact values in the number boxes.
Read the BMI number, the WHO category badge and the healthy weight range that corresponds to your height. Switch units at any time — the result is recomputed instantly.

Frequently asked questions

What are the WHO BMI categories?

Underweight: < 18.5. Normal: 18.5 - 24.9. Overweight: 25 - 29.9. Obesity class I: 30 - 34.9. Class II: 35 - 39.9. Class III: ≥ 40. These thresholds were set by the World Health Organization for adult populations of European descent.

Does BMI work for athletes?

Not very well. Muscle is denser than fat, so a strength athlete can land in the 'overweight' or 'obese' range despite very low body fat. For athletic populations, body-fat percentage (caliper, DEXA, BIA) and waist-to-height ratio give a more accurate picture.

Is BMI the same for men and women?

The thresholds are the same, but the same BMI corresponds to different body-fat percentages in men and women on average — women carry slightly more essential fat. Children and adolescents use age- and sex-adjusted percentile curves instead of these adult thresholds.

What's a 'healthy weight range' for my height?

The range that corresponds to a BMI between 18.5 and 24.9 for your height. The calculator shows the exact lower and upper weight values in your chosen unit. Hitting that range is associated with the lowest all-cause mortality risk in large epidemiological studies.

Should I use BMI or waist-to-hip ratio?

Both, ideally. BMI captures overall mass; waist-to-hip ratio captures fat distribution, which independently predicts cardiovascular risk. A normal BMI with a high waist-to-hip ratio is still a yellow flag worth discussing with a clinician.

Common use cases

Where a quick BMI check is genuinely useful.

Annual self check-up

Tracking your BMI yearly takes seconds and gives a coarse but consistent signal. Sudden moves up or down deserve a closer look.

Setting a fitness goal

Knowing your target healthy weight range helps frame realistic goals. The calculator shows the exact lower and upper weight for your height as a reference.

Insurance or medical forms

Many forms ask for BMI rather than asking for height and weight separately. Compute once, fill in the form correctly the first time.

Coaching or fitness apps

If your tracking app does not provide BMI directly, plug your values here to get the same number it would compute, useful for cross-referencing recommendations.

Tips and shortcuts

How to interpret BMI without overweighting it.

Trend matters more than the snapshot

A single BMI value is noise. Tracking the same number over months or years tells you whether you are drifting toward or away from your healthy range.

Pair BMI with waist measurement

Wrap a tape around your waist at navel height. Above 94 cm (37 in) for men or 80 cm (31.5 in) for women adds independent metabolic risk on top of BMI.

Don't trust BMI for kids or seniors

Pediatric BMI uses age- and sex-specific percentile curves, not adult cut-offs. Senior BMI tolerates a slightly higher range — some studies suggest 23-30 is healthier above 65 than the strict 18.5-24.9.

BMI is a screen, not a diagnosis

If your BMI flags an issue, talk to a doctor before making major lifestyle changes. Many factors (genetics, medications, body composition) can shift what 'healthy' means for you specifically.