BMI calculator (body mass index)

Name: BMI calculator
Author: Richard Injante

Your body mass index, your WHO category, the healthy weight range for your height and the waist-to-height ratio.

Content reviewed by Richard Injante Published by SolucionesAhora.com Updated on 2026-10-08 How we verify

Calculator inputs

Enter your figures, or press “See example” to watch it work.
If your case is unusual, open “Advanced options”.
Read the result and, below it, what it means and how it was worked out.

Weight

Your current weight, in kilograms (or pounds if you choose imperial units).

In kilograms or pounds

Height

Your height in centimetres (or inches with imperial units). If you enter metres (1.75) in the metric system, it is read correctly.

In centimetres or inches

Advanced options

Units (optional)

Metric (kilograms and centimetres) or imperial (pounds and inches).

Reference population (optional)

The WHO suggests lower cut-offs for Asian populations (overweight from 23, obesity from 27.5) because at the same BMI they carry more visceral fat and more cardiometabolic risk.

Waist (optional) (optional)

Waist circumference, measured at navel level, standing and after breathing out. It gives the waist-to-height ratio, which complements BMI because it reflects abdominal fat.

Circumference at navel level

See the result

Results

Body mass index22.9kg/m²

CategoryNormal weight

Healthy weight: minimum56.7

Healthy weight: maximum76.3

Difference from the healthy range0

See the working step by step

BMI = 22.9 kg/m²

Free, no sign-up! What if you could do this without a calculator? A five-minute game with challenges, lives and points. It clicks even when you cannot be bothered.

In short

What it calculates: Your body mass index, your WHO category, the healthy weight range for your height and the waist-to-height ratio.
Formula used: BMI = weight (kg) ÷ height (m)² (pounds: 703 × weight ÷ inches²)
Example: Example 1. Normal weight.

BMI calculator

Body mass index (BMI) relates your weight to your height and works as a first screen for underweight, overweight or obesity. It is quick and useful for populations, but it has limits: it cannot tell muscle from fat or where fat sits.

Enter your weight and height (in kilograms and centimetres, or pounds and inches). You get your BMI, the WHO category, the healthy weight range for your height and, if you add your waist, the waist-to-height ratio, which completes the picture because it reflects abdominal fat. Everything runs in your browser.

How it works

BMI is weight in kilograms divided by height in metres squared. The WHO classifies adults like this: underweight below 18.5; normal 18.5 to 24.9; overweight 25 to 29.9; and obesity from 30 (grades I, II and III). For Asian populations, the WHO suggests lower cut-offs (23 and 27.5).

The waist-to-height ratio divides waist circumference by height: a value below 0.5 is linked to lower cardiometabolic risk. It is a useful complement to BMI because abdominal fat weighs most in risk.

Formula

BMI = weight (kg) ÷ height (m)² (pounds: 703 × weight ÷ inches²)
Underweight < 18.5 · normal 18.5–24.9 · overweight 25–29.9 · obesity ≥ 30 (I 30–34.9 · II 35–39.9 · III ≥ 40)
Asian populations: normal 18.5–22.9 · overweight 23–27.4 · obesity ≥ 27.5
Healthy weight = BMI of 18.5 to 24.9 × height²
Waist-to-height ratio = waist ÷ height < 0.5 no added risk · 0.5–0.59 increased · ≥ 0.6 high

Worked example

Example 1. Normal weight.
At 70 kg and 175 cm, BMI is 70 ÷ 1.75² = 22.9: normal. The healthy range for that height is 56.7 to 76.3 kg.

Example 2. Overweight.
At 85 kg and 175 cm, BMI is 27.8: overweight. To get back to the healthy range (up to 76.3 kg) you would have to lose about 8.7 kg.

Example 3. With the waist.
At 80 kg, 175 cm and a 90 cm waist, BMI is 26.1 (overweight) and the waist-to-height ratio is 0.51: slightly above 0.5, a somewhat increased risk that BMI alone did not show.

Example 4. Asian population.
At 70 kg and 165 cm, BMI is 25.7. With the general cut-offs it is overweight, and with the Asian ones too (from 23), but with clearly increased risk.

Explanation

What BMI is and what it is for

It is a simple measure of the relationship between weight and height. It works as a first screen for underweight, overweight and obesity in adults, and for tracking trends in populations. It is not a diagnosis.

The WHO categories

- **Underweight**: below 18.5.
- **Normal**: 18.5 to 24.9.
- **Overweight**: 25 to 29.9.
- **Obesity**: 30 or more (grade I 30 to 34.9, grade II 35 to 39.9, grade III from 40).
For Asian populations lower cut-offs are used: overweight from 23 and obesity from 27.5.

Limits of BMI

It cannot tell **muscle from fat**: athletes and muscular people can have a high BMI without excess fat.
It does not say **where** fat sits: abdominal fat is the most linked to risk.
It can underestimate fat in **older adults** (because of muscle loss) and in some populations.
It does not apply to **children and teenagers**, who are assessed with percentiles, or to pregnant women.

Waist-to-height ratio

Dividing the waist by height is a simple measure of abdominal fat. A value below 0.5 is linked to lower cardiometabolic risk in adults of different ages and populations (Ashwell et al., 2012). It is a good complement to BMI.

Common mistakes

Reading BMI as a personal health grade.
Using height in inches with kilos (or the other way round).
Comparing yourself with the general cut-offs if you belong to an Asian population.
Forgetting body composition.

Limits of this calculator

For adults aged 18 or over; not for children, teenagers or pregnant women.
It does not account for muscle mass, age or fat distribution beyond the waist-to-height ratio.
It is indicative: it does not diagnose any condition.

Notice

This is an estimate and does not replace a health professional’s judgement. If your BMI is outside the normal range or your waist is large, see a doctor.

Frequently asked questions

What BMI is considered normal?

Between 18.5 and 24.9 according to the WHO. For Asian populations, the normal range is 18.5 to 22.9.

How is BMI calculated?

By dividing weight in kilograms by height in metres squared. For example, 70 kg and 1.75 m give 22.9.

Does BMI work for athletes?

With limits: muscle weighs more than fat, so an athlete can have a high BMI without excess fat. Look at waist or body-fat percentage too.

What is the waist-to-height ratio?

Waist divided by height. Below 0.5 is linked to lower cardiometabolic risk; it is a good complement to BMI.

Does it work for children?

No. For children and teenagers, percentiles by age and sex are used, not the adult cut-offs.

Why are there different cut-offs for Asian populations?

Because at the same BMI they carry more visceral fat and more cardiometabolic risk, and the WHO suggests lower cut-offs (23 and 27.5).

Does a high BMI mean I am ill?

Not necessarily: it is a risk indicator, not a diagnosis. A doctor also considers waist, blood tests and habits.

Is my data sent to a server?

No. The calculation runs in your browser.

Sources and references

The formula behind this calculator is not ours. These are the sources it comes from, in APA 7 format, in case you want to go to the original or cite them in your own work.

Organización Mundial de la Salud. (2000). Obesity: Preventing and managing the global epidemic (Informe técnico n.º 894). OMS. The BMI categories for adults.
WHO Expert Consultation. (2004). Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. The Lancet, 363(9403), 157–163. https://doi.org/10.1016/S0140-6736(03)15268-3 https://doi.org/10.1016/S0140-6736(03)15268-3 The cut-off points for Asian populations.
Ashwell, M., Gunn, P., & Gibson, S. (2012). Waist-to-height ratio is a better screening tool than waist circumference and BMI for adult cardiometabolic risk factors: Systematic review and meta-analysis. Obesity Reviews, 13(3), 275–286. https://doi.org/10.1111/j.1467-789X.2011.00952.x https://doi.org/10.1111/j.1467-789X.2011.00952.x The waist-to-height ratio and the 0.5 threshold.

Need to calculate something else?

These tools are often used alongside this calculator.