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BMI Calculator

Calculate Body Mass Index (BMI), healthy weight range, and WHO classification for adults.

Runs in your browser. Nothing you add is uploaded.

What the BMI Calculator does

Body mass index compares your weight with your height to give one number that doctors use as a first screen for underweight, healthy weight, overweight and obesity. Enter your height and weight in metric or imperial units and this calculator shows your BMI, its WHO category, the healthy weight range for your height and your BMI Prime — your BMI divided by 25, the top of the normal range. It is a quick screening measure, not a diagnosis, and the notes below explain where it is and is not reliable.

How to calculate your BMI

  1. Choose metric (centimetres and kilograms) or imperial (feet, inches and pounds).
  2. Enter your height and your weight, ideally measured in the morning without shoes.
  3. Read your BMI and the category it falls in.
  4. Check the healthy weight range for your height to see how far you are from it, if at all.
  5. Use BMI Prime to see the figure as a share of the upper healthy limit: 1.00 is exactly at the limit.

The BMI Calculator runs entirely in your browser — nothing you enter is uploaded, stored, or logged.

How it works

BMI Formula

BMI = weight (kg) / [height (m)]²

Body weight in kilograms divided by the square of height in meters.

Example: 70 kg / (1.75 m)² = 22.86 (Normal weight).

When to use it

A quick health check

Someone 170 cm tall and weighing 72 kg has a BMI of 24.9 — just inside the WHO healthy range, but above the 23 threshold many doctors use for South Asian adults. Knowing both numbers is a good prompt for a conversation with a doctor.

Setting a realistic target

The healthy weight range for 170 cm is about 53.5 to 72 kg. Seeing the range, rather than a single ideal number, makes it easier to set a goal that is achievable and sustainable.

Tracking change over time

BMI changes in the same direction as weight for adults, so recording it every few weeks shows the trend without needing any equipment beyond a scale.

Good to know

  • BMI does not distinguish muscle from fat. Athletes and people who do heavy strength training can have a high BMI with little body fat.
  • For South Asian adults, many doctors and Indian guidelines treat 23 or more as overweight and 25 or more as obese, because diabetes and heart risks rise at lower BMI.
  • Waist size adds information BMI misses: a waist above about 90 cm for men or 80 cm for women in Asian populations suggests excess abdominal fat.
  • Adult BMI categories do not apply to children and teenagers, who are assessed on age- and sex-specific growth charts.

Frequently asked questions

What is considered a normal BMI score?

According to the World Health Organization (WHO), a BMI between 18.5 and 24.9 is considered normal healthy weight for adults.

What is the BMI formula?

BMI = weight in kilograms ÷ (height in metres)². For 70 kg and 1.75 m that is 70 ÷ 3.0625 = 22.9. In imperial units the formula is 703 × weight in pounds ÷ (height in inches)².

What are the WHO BMI categories?

Below 18.5 is underweight, 18.5 to 24.9 is normal, 25 to 29.9 is overweight and 30 or above is obese, with obesity further divided into classes I (30–34.9), II (35–39.9) and III (40 and above).

Is BMI accurate during pregnancy or for older adults?

No, not on its own. Pregnancy weight gain is assessed differently, and in older adults a slightly higher BMI can be protective. Use the number as a starting point and ask a doctor what applies to you.

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