Toolnestly
Home/All tools/BMI Calculator
Free & unlimited

BMI Calculator

Check your body mass index from height and weight, in metric or imperial.

24.2
BMI
Normal weight

What this tool does

Calculates your body mass index (BMI) from height and weight, in metric or imperial units, and shows which standard adult weight category the result falls into.

Calculated instantly in your browser — nothing you enter is sent anywhere.

How to use this tool

1Choose metric (cm, kg) or imperial (ft & in, lb).
2Enter your height and weight.
3Read your BMI and the category it lands in — the result updates as you type.

The formula and the categories

BMI is weight in kilograms divided by height in metres squared. The imperial version multiplies by 703 so you can use pounds and inches directly — it's the same number either way.

  • Below 18.5 — Underweight
  • 18.5–24.9 — Normal weight
  • 25.0–29.9 — Overweight
  • 30.0 and above — Obese

What BMI doesn't tell you

BMI is a population-level screening number, not a measure of health or body composition. It doesn't distinguish muscle from fat or account for where fat is carried, so it's least reliable for:

  • Very muscular people, who often read as “overweight” with low body fat
  • Older adults, who lose muscle and may be under-flagged
  • Children and teens, who need age- and sex-specific BMI percentiles, not these adult bands
  • Pregnant people, for whom standard BMI doesn't apply

Treat it as one rough data point. Waist measurement, blood pressure, blood work, and a conversation with a doctor say far more about health.

FAQ

Is BMI an accurate measure of health?
No — it's a quick screen, not a diagnosis. It estimates body size relative to height for an average adult and ignores muscle, fat distribution, age, and sex. Use it as a starting point, not a verdict.
What formula does this use?
weight (kg) ÷ height (m)². The imperial mode uses 703 × weight (lb) ÷ height (in)², which is mathematically the same, just skipping a unit conversion.
Can I use this for my child?
Not with these categories. Children and teens are assessed against age- and sex-specific percentile charts — ask a paediatrician or use a dedicated child BMI-percentile tool.
My BMI says overweight but I'm fit — what gives?
Muscle is denser than fat, so athletes and heavy lifters routinely score in the overweight range with low body fat. This is the best-known limitation of BMI.
Is my data sent anywhere?
No. Everything is calculated locally in your browser and never leaves your device.

Related tools

Mortgage Calculator→Unit Converter→All tools→