How to use the bmi calculator
- Choose metric (cm, kg) or imperial (feet and inches, pounds or stone).
- Enter your height and weight. Optionally add your waist measurement for the waist-to-height ratio.
- Read your BMI, its category, and the healthy weight range for your height. Switch to the Asian cut-offs if they apply to you.
What BMI measures
Body mass index was devised by the Belgian statistician Adolphe Quetelet in the 1830s and adopted for public health in the 1970s because it is quick, free and correlates reasonably well with body fat across large groups. It is a screening number: doctors use it to decide who might benefit from a closer look at blood pressure, blood sugar and cholesterol, not to diagnose anything.
BMI = weight (kg) ÷ height (m)² · BMI = 703 × weight (lb) ÷ height (in)²
The categories
| Category | WHO (most adults) | Asian cut-offs |
|---|---|---|
| Underweight | under 18.5 | under 18.5 |
| Healthy weight | 18.5 – 24.9 | 18.5 – 22.9 |
| Overweight | 25 – 29.9 | 23 – 27.4 |
| Obese | 30 and over | 27.5 and over |
The US CDC, the UK NHS, Health Canada and Australia's Department of Health all use the WHO ranges for adults. Singapore's Health Promotion Board uses the Asian action points, and the UK's NICE guidance (2022) recommends the lower thresholds for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background.
The healthy weight range for your height
The range shown is simply the BMI formula run backwards: the weight that gives a BMI of 18.5 at your height, up to the weight that gives 24.9 (or 22.9 on the Asian scale). For someone 5 ft 9 in tall that is about 125 to 169 lb; for 175 cm it is about 57 to 76.5 kg. It is a broad band on purpose, because frame size, muscle and age all shift where a given person is healthiest.
Where BMI falls short, and what to add
BMI treats a kilogram of muscle the same as a kilogram of fat and says nothing about where fat is carried. Fat around the abdomen is the type most linked to diabetes and heart disease. That is why the waist-to-height ratio is shown when you enter a waist measurement: keep your waist to less than half your height. Measure around the bare waist, midway between the lowest rib and the top of the hip bone (roughly at the navel), after breathing out.
BMI Prime is your BMI divided by the upper limit of the healthy range. 1.00 is the top of the healthy range, and 1.20 is 20% above it. It is a convenient way to see how far from the boundary a number sits, whichever scale you use.
General information only, not medical advice. If you are concerned about your weight, your eating, or your health, speak to a doctor, GP or registered dietitian.
Questions and answers
How is BMI calculated?
BMI is weight in kilograms divided by height in metres squared. Someone 1.75 m tall weighing 70 kg has a BMI of 70 ÷ (1.75 × 1.75) = 22.9. In pounds and inches the formula is 703 × lb ÷ in²: 5 ft 9 in (69 in) and 154 lb gives 703 × 154 ÷ 4,761 = 22.7.
What is a healthy BMI?
For adults, the World Health Organization classes 18.5 to 24.9 as a healthy weight, 25 to 29.9 as overweight and 30 or above as obese (class 1: 30–34.9, class 2: 35–39.9, class 3: 40+). Below 18.5 is underweight. These are population screening ranges; they say nothing certain about any one person's health.
Why are there different cut-offs for Asian people?
People of Asian descent tend to have a higher risk of type 2 diabetes and heart disease at a lower BMI. A WHO expert consultation in 2004 proposed action points of 23 and 27.5, and these are used by Singapore's Health Promotion Board and recommended by the UK's NICE for people of South Asian, Chinese, other Asian, Middle Eastern, Black African and African-Caribbean family background. Choose 'Asian' in the calculator to apply them.
Is BMI accurate for athletes or older people?
Not very. BMI cannot tell muscle from fat, so muscular people can read as overweight while being lean, and older adults who have lost muscle can read as healthy while carrying excess fat. Waist measurement adds useful information: NICE advises keeping waist circumference below half your height (a waist-to-height ratio under 0.5).
Can I use this for a child or teenager?
No. For under-18s, BMI has to be compared with growth charts for the child's exact age and sex (BMI-for-age percentiles from the CDC in the US, or the UK90 charts in the UK). The adult categories here do not apply. A paediatrician, school nurse or GP can do this properly.
Is BMI valid during pregnancy?
No. Use your pre-pregnancy weight if a midwife or doctor asks for your BMI; weight gain in pregnancy is assessed differently.
Free to use, runs in your browser, nothing uploaded. Last updated 2026-10-07. Made by HandyToolkits; questions to [email protected].