BMI calculator · Free · No sign-up
BMI Calculator
BMI, or body mass index, is weight in kilograms divided by height in metres squared. For adults, a BMI under 18.5 is underweight, 18.5 to 24.9 is a healthy weight, 25 to 29.9 is overweight and 30 or more is obesity, using the WHO and CDC categories. It is a screening number, not a diagnosis.
This page also shows the weights at your height.
A screening number, not a diagnosis. It cannot tell muscle from fat, and it is not for anyone under 20 or for pregnancy.
- BMI
- 22.9 kg/m²
- Category
- Healthy weight
- Weight at BMI 18.5 to 25
- 56.7 kg to under 76.6 kg
- Your weight against that
- Inside it
| Category | BMI | Weight at your height | |
|---|---|---|---|
| Underweight | under 18.5 | under 56.7 kg | |
| Healthy weight | 18.5 to under 25 | 56.7 kg to under 76.6 kg | You are here |
| Overweight | 25 to under 30 | 76.6 kg to under 91.9 kg | |
| Obesity class 1 | 30 to under 35 | 91.9 kg to under 107.2 kg | |
| Obesity class 2 | 35 to under 40 | 107.2 kg to under 122.5 kg | |
| Obesity class 3 | 40 or more | 122.5 kg or more |
The CDC applies these categories to every adult aged 20 and over, whatever their age, sex or race.
The figures above are an example: put in your own. Worked out in this browser and kept there; nothing is sent anywhere. To count the training behind the number, try the training volume calculator.
Choose your units, enter your height, weight and age, and the BMI appears with its adult category and the weight range that each category means at your height. You can switch to the WHO’s Asian action points. It does nothing for anyone under 20.
BMI (body mass index) is a person’s weight in kilograms divided by the square of their height in metres. It is a quick screening measure of weight for height, not a measure of body fat.
- No sign-up
- Nothing uploaded
- WHO and CDC categories
- Works offline
- Shows its working
Key facts
| Detail | Answer |
|---|---|
| Price | Free, no sign-up, nothing to install |
| Formula | kg ÷ m², or 703 × lb ÷ in² |
| Adult categories | Under 18.5, 18.5 to 24.9, 25 to 29.9, 30 or more; obesity classes at 30, 35 and 40 |
| Asian action points | 23, 27.5, 32.5 and 37.5 (WHO expert consultation, 2004) |
| Who it is for | Adults aged 20 and over; children and teenagers need growth charts |
| Where the figures come from | CDC “Adult BMI Categories” and WHO Global Health Observatory, read 3 November 2026 |
| Where your numbers are kept | This browser only |
How to calculate your BMI
Enter your measurements, then read the number and the table.
Choose your units
Metric, US or UK; the height and weight boxes change to match.
Enter your height and weight
Centimetres and kilograms, or feet, inches and pounds, or stones and pounds.
Enter your age
The adult table is for 20 and over; for a younger age the page says so and stops.
Choose the categories
WHO and CDC adult by default, or the WHO Asian action points.
Read the result
The BMI, its category and the weight range at your height, with the row you are in marked.
Treat it as a starting point
It is a screening number; a clinician can say what it means for you.
Who uses a BMI calculator
Anyone who has a height and a weight and wants the number, the category and the working behind it.
Adults checking a number
A quick figure and the category it falls in, in the units on the scales.
People who weigh in stones
Stones and pounds taken in directly, with no conversion first.
Anyone asked for a BMI on a form
The number to one decimal, as it is usually written.
People from Asian backgrounds
The WHO action points shown beside the standard categories.
Fitness trackers
The weight range at their height, to read alongside training logs.
Students
The formula, a worked example and the unit factors, with the rounding rule stated.
Healthy weight range by height
The usual question is not “what is my BMI” but “what would I weigh at this BMI”. The calculator above answers that for your exact height. This table gives the same figure for common heights: the weights at which BMI is 18.5 and 25, which are the two ends of the healthy weight category.
| Height | Kilograms | Pounds | Stones and pounds |
|---|---|---|---|
| 150 cm (4 ft 11 in) | 41.6 to 56.2 | 91.8 to 124.0 | 6 st 8 lb to 8 st 12 lb |
| 155 cm (5 ft 1 in) | 44.4 to 60.1 | 98.0 to 132.4 | 7 st 0 lb to 9 st 6 lb |
| 160 cm (5 ft 3 in) | 47.4 to 64.0 | 104.4 to 141.1 | 7 st 6 lb to 10 st 1 lb |
| 165 cm (5 ft 5 in) | 50.4 to 68.1 | 111.0 to 150.1 | 7 st 13 lb to 10 st 10 lb |
| 170 cm (5 ft 7 in) | 53.5 to 72.2 | 117.9 to 159.3 | 8 st 6 lb to 11 st 5 lb |
| 175 cm (5 ft 9 in) | 56.7 to 76.6 | 124.9 to 168.8 | 8 st 13 lb to 12 st 1 lb |
| 180 cm (5 ft 11 in) | 59.9 to 81.0 | 132.1 to 178.6 | 9 st 6 lb to 12 st 11 lb |
| 185 cm (6 ft 1 in) | 63.3 to 85.6 | 139.6 to 188.6 | 10 st 0 lb to 13 st 7 lb |
| 190 cm (6 ft 3 in) | 66.8 to 90.2 | 147.2 to 199.0 | 10 st 7 lb to 14 st 3 lb |
| 195 cm (6 ft 5 in) | 70.3 to 95.1 | 155.1 to 209.6 | 11 st 1 lb to 15 st 0 lb |
The top of each range is the weight at which BMI reaches 25, so it is not itself part of the healthy category. Weights are rounded for reading; the calculator above works from your exact entry. The band is 15 to 25 kg (33 to 55 lb) wide across these heights, which is the point of the table: even inside the category, BMI does not pick one weight.
How BMI is calculated
BMI is weight divided by height squared. In metric units that is kilograms divided by metres squared. In pounds and inches it is the same sum with a factor to convert the units: 703 × pounds ÷ inches squared. The answer is written in kg/m², although the unit is rarely shown.
| Units | Formula | Worked example |
|---|---|---|
| Metric | kg ÷ (m × m) | 70 ÷ (1.75 × 1.75) = 22.9 |
| US | 703 × lb ÷ (in × in) | 703 × 154 ÷ (69 × 69) = 22.7 |
| UK | kg ÷ (m × m), after changing stones and pounds to kilograms | 11 st = 154 lb = 69.9 kg; 69.9 ÷ 3.0625 = 22.8 |
The three results differ in the last digit because 154 lb is 69.85 kg, not 70, and 5 ft 9 in is 175.26 cm, not 175. The calculator works from the exact figures (1 lb is 0.45359237 kg and 1 in is 2.54 cm exactly), so it does not add a rounding error of its own. The 703 in the pounds formula is itself a rounded factor, about 703.07, so the page converts to kilograms first.
Rounding decides the category. The BMI is rounded to one decimal place, and the category is read from that rounded number, so the figure on screen and the category always agree. A BMI of 24.96 shows as 25.0 and is called overweight. The weights in the table are for a BMI exactly on the boundary, so a weight a fraction under one can still show the next category.
The adult BMI categories
The adult categories are the same two sets of numbers from the WHO and from the CDC, and they are the default here. The WHO’s data pages define underweight as a BMI under 18.5, overweight as 25 or more and obesity as 30 or more. The CDC’s adult page adds the names for the middle and the classes of obesity.
| Category | BMI (kg/m²) |
|---|---|
| Underweight | Less than 18.5 |
| Healthy weight | 18.5 to less than 25 |
| Overweight | 25 to less than 30 |
| Obesity | 30 or greater |
| Class 1 | 30 to less than 35 |
| Class 2 | 35 to less than 40 |
| Class 3 (severe) | 40 or greater |
Two wording points. The CDC says healthy weight where older WHO tables say normal; the range is the same, 18.5 to 24.9. And the CDC states that for adults of 20 and older the categories are “based on a person’s BMI regardless of age, sex, or race”, which is the rule this calculator follows by default. The next section is about the one place the WHO itself says otherwise.
The WHO Asian action points
In 2004 a WHO expert consultation, published in The Lancet (volume 363, pages 157 to 163), looked at whether the standard cut-offs suit Asian populations, where risk of type 2 diabetes and cardiovascular disease was seen at lower BMIs. It did not replace 18.5, 25 and 30, which it kept as the international classification for comparing countries. It added four action points for public health: 23, 27.5, 32.5 and 37.5.
| Standard (WHO and CDC) | Asian action points (WHO 2004) |
|---|---|
| Underweight: under 18.5 | Underweight: under 18.5 |
| Healthy weight: 18.5 to under 25 | Below the first action point: 18.5 to under 23 |
| Overweight: 25 to under 30 | First action point: 23 to under 27.5 |
| Obesity class 1: 30 to under 35 | Second action point: 27.5 to under 32.5 |
| Obesity class 2: 35 to under 40 | Third action point: 32.5 to under 37.5 |
| Obesity class 3: 40 or more | Fourth action point: 37.5 or more |
Choose WHO Asian action points in the Categories box to see the second column applied to your own numbers. The bands are named for the point they pass, not given a verdict, because the consultation described them as trigger points for public health action and not as a classification of individuals. Whether they matter for you is a question for a clinician who knows your history.
Why there is no result under 20
This calculator will not give a category to anyone under 20, and that is deliberate. The CDC’s adult categories are for ages 20 and older, and it points ages 2 to 19 to a separate calculator, because a child’s BMI is read against growth charts for their age and sex. The CDC groups the result by percentile: under the 5th is underweight, 5th to under the 85th is a healthy weight, 85th to under the 95th is overweight and the 95th or above is obesity.
The WHO does the same by standard deviation from the median: thinness is more than 2 below it, overweight more than 1 above and obesity more than 2 above. Neither uses 18.5 or 25. A 12-year-old with a BMI of 22 is not in the same place as a 30-year-old with a BMI of 22, which is why the page asks for age and stops rather than guess.
What BMI does not tell you
BMI uses two measurements, so it is blind to everything else. The CDC calls it “one potential health indicator” that “should be considered with other factors”. In practice that means:
| Situation | Why the number can mislead |
|---|---|
| Muscular people | Muscle weighs more than fat for the same volume, so a trained person can reach a high BMI with little body fat. |
| Pregnancy | Weight rises for reasons the formula does not model; it is not for use during pregnancy. |
| Children and teenagers | Need growth charts, as above. |
| Where weight is carried | Two people with the same BMI can carry weight in different places; BMI cannot see that. |
| Different populations | The WHO’s Asian action points exist because the standard cut-offs may not match risk everywhere. |
None of this means BMI is useless: it is a quick, free screening number that is comparable across millions of people. It means the number starts a conversation and does not end it.
What this calculator does not do
This is a calculator for one number. It does not give medical advice and it does not replace a clinician.
| It does | It does not |
|---|---|
| Work out BMI from height and weight in metric, US or UK units | Say whether your weight is right for you |
| Sort it into the WHO and CDC adult categories, or the WHO Asian action points | Diagnose, or suggest a diet, a target or a treatment |
| Show the weights that bound each category at your height | Measure body fat, muscle or where weight is carried |
| Refuse an age under 20, with the reason | Calculate for children, teenagers or pregnancy |
| Keep your entries in this browser | Send your height, weight or age anywhere |
This calculator or a bare BMI formula
What this page adds to the bare BMI sum.
| This calculator | A bare BMI formula | |
|---|---|---|
| Cost | Free, no sign-up | Free |
| Metric, US and UK units | Yes, including stones | One system |
| Weight range at your height | Yes, for every category | No |
| WHO Asian action points | Optional, labelled as action points | No |
| Says who the table is for | Yes: 20 and over, and refuses younger ages | No |
| Shows its working | Formula, rounding and exact unit factors | The formula |
| Your numbers leave the browser | Never | Varies |
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Frequently asked questions
What is BMI?
BMI, or body mass index, is a person’s weight in kilograms divided by their height in metres squared. It gives one number for weight relative to height. It is used as a screening measure for adults, and it does not measure body fat or say anything about health on its own.
How do you calculate BMI?
Divide your weight in kilograms by your height in metres, squared. A person of 70 kg and 1.75 m has a BMI of 70 ÷ 3.0625, which is 22.9. In pounds and inches, multiply the weight in pounds by 703 and divide by the height in inches squared.
What is a healthy BMI?
For adults aged 20 and over, the CDC calls a BMI from 18.5 to less than 25 a healthy weight. Under 18.5 is underweight, 25 to less than 30 is overweight and 30 or more is obesity. It is a screening range, and the right figure for one person depends on factors BMI cannot see.
What BMI is obese?
A BMI of 30 or more is obesity for adults, split by the CDC into class 1 (30 to less than 35), class 2 (35 to less than 40) and class 3, or severe obesity (40 or more). The WHO uses the same 30 cut-off. BMI is a screening number, not a diagnosis.
Is BMI different for Asian people?
A 2004 WHO expert consultation kept 18.5, 25 and 30 as the international classification but added action points at 23, 27.5, 32.5 and 37.5, because risk of type 2 diabetes and heart disease was seen at lower BMIs in Asian populations. The CDC’s adult categories do not change by race.
Is BMI accurate for athletes or muscular people?
Not always. BMI only uses height and weight, and muscle weighs more than fat, so a muscular person can have a BMI in the overweight range with little body fat. The CDC says BMI should be considered with other factors, and a clinician can use measures that BMI lacks.
Is there a BMI calculator for children and teenagers?
Children and teenagers aged 2 to 19 are not sorted by the adult table. The CDC reads their BMI as a percentile for age and sex: under the 5th is underweight, 5th to under the 85th is healthy, 85th to under the 95th is overweight and the 95th or above is obesity. This page does not calculate it.
How do I work out my BMI in stones and pounds?
Change stones and pounds to pounds by multiplying the stones by 14 and adding the pounds, then convert to kilograms by multiplying by 0.45359237. Divide that by your height in metres squared. This page does it for you: choose UK units and type the stones and pounds in directly.
Related guides
Longer answers to the questions behind the numbers.