MultiConvers

BMI Calculator

Compute adult body mass index from the weight and height you type — kilograms and centimetres, or pounds with feet and inches — then place the number on the WHO adult bands. It is a screening ratio, not a diagnosis and not a body-fat percentage.

Updated

How to use

  1. Choose metric (kg and cm) or US units (lb, feet and inches) so the fields match the tape and scale you have.
  2. Enter current weight. Height in centimetres is converted to metres (175 cm is 1.75 m) before the division.
  3. Read BMI to two decimals and the WHO adult label that band uses on this page.
  4. If you want the weight range that maps to BMI 18.5–24.9 at this height, open Healthy Weight. For tape-based fat percent, use Body Fat.

How it works

Body mass index is weight divided by height squared. In SI units that is kilograms over metres squared. A person at 70 kg and 175 cm is 70 ÷ (1.75 × 1.75) ≈ 22.86, which this page labels healthy weight because it sits in 18.5–24.9. Pounds and inches are converted first; that path is algebraically the same as the familiar 703 × lb / in² shortcut.

The category labels are the WHO adult cut-offs published for population screening: underweight below 18.5, healthy 18.5–24.9, overweight 25–29.9, obesity 30 and above. This page does not split obesity into class I–III, does not apply child or adolescent centiles, and does not use ethnicity-specific thresholds that some clinics discuss. A number that is “overweight” here is a band label, not a sentence about your health.

BMI cannot see muscle, bone density, oedema, pregnancy or where fat sits. Two people can share 27.7 and look nothing alike. Athletes often land in overweight while carrying little fat; older adults can sit in the “healthy” band with low muscle. That is why a tape estimate (Navy method) or a clinical measurement is a different question — and why this calculator shows a disclaimer.

Use the number as a quick consistency check against a chart, a form that asks for BMI, or the Healthy Weight range for the same height. Do not treat a tenth of a point as a verdict. Scales vary; height changes a little through the day; the formula is exact for the inputs, not for the person.

This is not medical advice and not a treatment plan. If a clinician has told you to ignore BMI or to use a different index, follow that. The related Ideal Weight page is Devine’s height-only equation, which is not the same as this ratio.

Formula

BMI = kg / m²
BMI = 703 × lb / in²

Worked examples

  • A metric example

    70 kg, 175 cm → BMI ≈ 22.9 (healthy weight)

  • 80 kg at 170 cm

    80 kg, 170 cm → BMI ≈ 27.7 (overweight)

  • A US example

    154 lb, 5 ft 9 in → BMI ≈ 22.7 (healthy weight)

WHO adult BMI categories

Adult cut-offs used by this calculator. Not for children.
BMICategory
Less than 18.5Underweight (WHO < 18.5)
18.5–24.9Healthy weight (WHO 18.5–24.9)
25–29.9Overweight (WHO 25–29.9)
30 or moreObesity (WHO ≥ 30)

Useful notes

  • WHO cut-offs are for adults. They are not applied to children on this page.
  • BMI is not body fat and not a diagnosis.
  • Not medical advice.

FAQ

How do I calculate BMI?

Divide weight in kilograms by height in metres squared.

How do I calculate BMI with kg and cm?

Convert height to metres (divide cm by 100), then divide weight in kilograms by height squared. 70 kg at 175 cm is 70 / 1.75² ≈ 22.9.

Is BMI the same as body fat?

No. BMI uses only height and weight. A tape or DEXA estimate of fat is a different measurement.

Is this a diagnosis?

No. It is a published index with known limits, not a clinical opinion.

Why does 80 kg at 170 cm show overweight?

80 ÷ 1.70² ≈ 27.7, which is inside the WHO 25–29.9 band this page labels overweight. That label is the cut-off, not a clinical exam.

Can I use this for a child?

No. Child BMI is plotted on age-and-sex centiles. This page only applies adult WHO cut-offs.

Guides

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