Body mass index is the most widely used screening number in public health because it needs only two measurements you can take at home. It compares your weight with your height and places the result on a scale that health agencies use to flag possible underweight, overweight and obesity. This calculator gives the number, the category it falls in, and the range of weights that would put a person of your height inside the healthy band, so you can see how far you are from it in kilograms or pounds rather than as an abstract index.
BMI is a screening tool, not a diagnosis. It says nothing about where fat is stored, how much muscle you carry or how fit you are. Read it alongside a waist measurement and, if you have concerns, with a clinician.
How to use the BMI calculator
- Enter your height in centimetres, metres, inches or feet. Use the unit menu beside the box.
- Enter your weight in kilograms, pounds, grams or ounces. Weigh yourself in the morning, before eating, for the most consistent figure.
- Enter your age. The categories apply from 18 years. For younger people see the Child & Teen BMI Calculator.
- Pick a category scale. Use the WHO standard cut-offs unless you are of South or East Asian background and want the lower WHO action points.
- Read the results: BMI, category, healthy weight range, and how many kilograms above or below that range you are.
BMI formula
BMI = 703 × weight (lb) ÷ height (in)²
Weight at a target BMI = target BMI × height (m)²
The index goes back to the Belgian mathematician Adolphe Quetelet in the 1830s, and the name “body mass index” was proposed by Ancel Keys and colleagues in 1972. The adult cut-offs used here are those of the World Health Organization (Obesity: preventing and managing the global epidemic, WHO Technical Report Series 894, 2000), which the US Centers for Disease Control and Prevention also uses for adults.
| BMI (kg/m²) | WHO category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obesity class I |
| 35.0 – 39.9 | Obesity class II |
| 40.0 and above | Obesity class III |
Worked example
A person is 170 cm (1.70 m) tall and weighs 70 kg.
- Height squared: 1.70 × 1.70 = 2.89
- BMI: 70 ÷ 2.89 = 24.2, which is in the normal weight band.
- Lower end of the healthy range: 18.5 × 2.89 = 53.5 kg
- Upper end: 24.9 × 2.89 = 72.0 kg
- BMI 30 would be reached at 30 × 2.89 = 86.7 kg.
Weights for common BMI cut-offs by height
Each weight below is the cut-off BMI multiplied by height squared, calculated for you in kilograms and pounds.
| Height | BMI 18.5 (lower end of healthy range) | BMI 25 (overweight begins) | BMI 30 (obesity begins) |
|---|---|---|---|
| 150 cm (4′11″) | 41.6 kg (92 lb) | 56.2 kg (124 lb) | 67.5 kg (149 lb) |
| 155 cm (5′1″) | 44.4 kg (98 lb) | 60.1 kg (132 lb) | 72.1 kg (159 lb) |
| 160 cm (5′3″) | 47.4 kg (104 lb) | 64.0 kg (141 lb) | 76.8 kg (169 lb) |
| 165 cm (5′5″) | 50.4 kg (111 lb) | 68.1 kg (150 lb) | 81.7 kg (180 lb) |
| 170 cm (5′7″) | 53.5 kg (118 lb) | 72.2 kg (159 lb) | 86.7 kg (191 lb) |
| 175 cm (5′9″) | 56.7 kg (125 lb) | 76.6 kg (169 lb) | 91.9 kg (203 lb) |
| 180 cm (5′11″) | 59.9 kg (132 lb) | 81.0 kg (179 lb) | 97.2 kg (214 lb) |
| 185 cm (6′1″) | 63.3 kg (140 lb) | 85.6 kg (189 lb) | 102.7 kg (226 lb) |
| 190 cm (6′3″) | 66.8 kg (147 lb) | 90.2 kg (199 lb) | 108.3 kg (239 lb) |
| 195 cm (6′5″) | 70.3 kg (155 lb) | 95.1 kg (210 lb) | 114.1 kg (251 lb) |
The Asian cut-off option
In 2004 a WHO expert consultation reviewed evidence that the relationship between BMI, body fat and disease risk differs between populations (WHO Expert Consultation, Lancet 2004;363:157–163). In many Asian groups, risk of type 2 diabetes and cardiovascular disease rises at lower BMI values than in European groups. The panel kept 18.5 as the underweight limit and 25 and 30 as international reference points, but recommended that countries also report two further public-health action points: 23.0 and 27.5. When you choose the Asian scale this calculator labels 18.5–22.9 as the normal range, 23.0–27.4 as increased risk, and 27.5 or more as high risk. The healthy range is then capped at a BMI of 22.9.
Limits of BMI
- It does not measure fat. Muscle is denser than fat, so strength athletes can have a high BMI and low body fat.
- It ignores distribution. Fat around the abdomen carries more risk than fat on the hips and thighs. A waist-to-height ratio captures this; see the Waist-to-Height Ratio Calculator.
- Age and height matter. Older adults lose muscle and height, and very short or very tall people can be misclassified.
- It is a population tool. Categories describe average risk in groups, not the health of one person.
For a better picture of body composition try the Body Fat Calculator or the Relative Fat Mass (RFM) Calculator, and for a target weight see the Ideal Weight Calculator. This page is for information only and is not medical advice.
Sources
- World Health Organization. Obesity: preventing and managing the global epidemic. WHO Technical Report Series 894, 2000.
- WHO Expert Consultation. Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. Lancet 2004;363:157–163.
- US Centers for Disease Control and Prevention. About Adult BMI.
- US National Heart, Lung, and Blood Institute. Calculate Your Body Mass Index (imperial formula 703 × lb ÷ in²).
- Keys A, et al. Indices of relative weight and obesity. J Chronic Dis 1972;25:329–343.
Frequently asked questions
How is BMI calculated?
BMI is weight in kilograms divided by height in metres squared. A person who weighs 70 kg and is 1.70 m tall has a BMI of 70 ÷ 2.89 = 24.2. In pounds and inches the same value is 703 × weight ÷ height², the form used by the US National Heart, Lung, and Blood Institute.
What is a healthy BMI?
The World Health Organization defines a normal range of 18.5 to 24.9 for adults. At 1.70 m that corresponds to roughly 53.5 to 72.0 kg. A value in this range is associated with the lowest average risk at population level, but it does not guarantee good health for any one person.
Why is there an Asian option?
A 2004 WHO expert consultation found that many Asian populations carry more body fat and a higher risk of type 2 diabetes and heart disease at a lower BMI than Europeans. It proposed extra public-health action points at 23.0 and 27.5. The option applies those bands; it does not change the BMI figure itself.
Is BMI accurate for athletes or older adults?
Not always. BMI cannot tell muscle from fat, so a muscular person can score as overweight with little excess fat, and older adults who have lost muscle can look normal while carrying more fat than the number suggests. A waist measurement or body-fat estimate adds useful context.
Can I use this for my child?
No. Children and teenagers are judged against age- and sex-specific percentile charts, not the fixed adult cut-offs. A child’s BMI that would be “overweight” in an adult may be perfectly typical for their age.