WiseCalcs

BMI calculator

Enter your height and weight, choose metric or imperial, and see your adult BMI category plus the mathematical weight interval for BMI 18.5–24.9.

Written by Kenneth Schrøder, Founder of WiseCalcs

Updated ·Sources verified

For adults aged 18 and over, this calculator applies the WHO BMI categories; 18.5–24.9 is the normal BMI range.

cm
kg

Your BMI

22.9

Normal weight

Weight at BMI 18.5–24.9: 56.7–76.3 kg

The gauge classifies the result with the WHO adult bands. The weight interval is only the BMI formula solved for 18.5–24.9 at your height, not personal health advice.

How does it work?

Imperial entries are converted to kilograms and metres first. WHO bands: under 18.5, 18.5–24.9, 25–29.9, 30 and over.

BMI formula

BMI=weight (kg)height (m)2\text{BMI} = \dfrac{\text{weight (kg)}}{\text{height (m)}^2}
weight
Body weight in kilograms.
height
Standing height in metres.

A person of 70 kg and 1.75 m has a BMI of 70 ÷ 1.75² ≈ 22.9 (normal).

Expert tips

  • BMI does not directly measure body fat, and the same BMI can represent different fatness or risk across people and populations.
  • BMI is a population-level screening classification, not an individual diagnosis or target weight.

Method & sources

We divide weight in kilograms by height in metres squared and compare the result with WHO adult categories for ages 18 and over. The displayed weight interval is only the BMI formula rearranged at 18.5 and 24.9; it is not a personal target or diagnosis.

Sources

Where this method comes from — use these references to understand the formula, assumptions, and limits.

How we calculate

  • Uses the WHO adult cut-offs: underweight under 18.5, normal 18.5–24.9, overweight 25–29.9, obese 30 and over.
  • BMI screens for weight relative to height; it does not measure body fat or distinguish muscle from fat.
  • The fixed bands are for adults aged 18 and over and are not adjusted for children, pregnancy, body composition, or population differences.

Limitations

  • BMI does not directly measure body fat, and the same BMI can represent different fatness or risk across people and populations.
  • BMI is a population-level screening classification, not an individual diagnosis or target weight.

Rounding

BMI is shown to one decimal place. Imperial entries are converted to kilograms (1 lb = 0.45359237 kg) and metres (1 in = 0.0254 m) before the standard metric formula is applied.

What BMI tells you

Body Mass Index (BMI) compares weight with height and places the result in an adult classification. WHO uses fixed adult thresholds from age 18, but BMI is a surrogate marker: it does not directly measure body fat or diagnose an individual's health.

How to use it

  1. Choose metric (cm, kg) or imperial (in, lb).
  2. Enter your height.
  3. Enter your weight.
  4. Read your BMI, category and the mathematical weight interval at BMI 18.5–24.9.

The WHO weight categories

  • Underweight: BMI below 18.5
  • Normal weight: BMI 18.5 to 24.9
  • Overweight: BMI 25 to 29.9
  • Obese: BMI 30 and over

A worked example

Someone 1.75 m tall weighing 70 kg has a BMI of 70 ÷ 1.75² ≈ 22.9, which is in the normal range. Rearranging the same formula gives roughly 57–76 kg at BMI 18.5–24.9 for that height; this is a mathematical interval, not a recommended target.

Why BMI has limits

BMI does not separate muscle from fat or show fat distribution. WHO notes that the same BMI may reflect different fatness and risk across people and populations. Children need age-specific BMI, while an adult may use a body-fat or waist-related measure for a different view.

FAQ

How is BMI calculated?
BMI is your weight in kilograms divided by the square of your height in metres. Imperial entries are converted to kilograms and metres first.
What is the WHO normal BMI range for adults?
For adults aged 18 and over, WHO classifies BMI 18.5–24.9 as normal. That category is not a personal diagnosis or proof of health.
Does BMI work for athletes?
Not well. BMI does not distinguish muscle mass from fat mass, so very muscular people can land in the overweight band despite low body fat. Pair BMI with a body-fat estimate.
Is BMI suitable for children?
No. Children and teenagers use age- and sex-specific BMI percentiles instead of the fixed adult cut-offs used here.
Can I switch between metric and imperial?
Yes. Pick the unit system at the top and enter height and weight in those units; the result is the same BMI either way.
Can I share my result?
Yes. Use Share to copy a link that reopens the calculator with the same height, weight and units.

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