FizzyTools
BMI calculator
Work out your body mass index in any units, for adults or children, with your healthy weight range. Free, no sign-up, and your measurements never leave your device.
How it works
- 1Enter height and weightIn cm, feet, kg, pounds or stones, as you know them.
- 2See your BMIWith what it means and your healthy weight range, as you type.
- 3Copy or shareCopy the result, or a link that opens the same measurements.
Formulas and sources
- BMI
- weight (kg) ÷ height (m)²; in pounds and inches: 703 × lb ÷ in²
- Adult categories
- under 18.5 underweight (below 16, 17 and 18.5: severe, moderate and mild thinness) · 18.5–24.9 healthy weight · 25–29.9 overweight · 30–34.9, 35–39.9 and 40 or more obesity classes 1, 2 and 3
- Lower cut-offs
- 18.5–22.9 healthy weight · 23–27.4 overweight · 27.5 or more obesity (classes from 27.5, 32.5 and 37.5)
- India
- 18–22.9 healthy weight · 23–24.9 overweight · 25 or more obesity
- Children (2–19)
- BMI-for-age percentile for the child's sex: under the 5th underweight · 5th to under 85th healthy weight · 85th to under 95th overweight · 95th or more obesity · 120 % of the 95th or a BMI of 35 or more severe obesity
- Waist-to-height
- waist ÷ height: 0.4–0.49 no increased health risk · 0.5–0.59 increased · 0.6 or more further increased
- BMI Prime
- BMI ÷ 25
- Ponderal index
- weight (kg) ÷ height (m)³
Sources: CDC adult BMI categories and WHO; CDC child and teen BMI categories with the CDC extended BMI-for-age charts (2022); lower cut-offs and waist: NICE CG189 (2022 update), from the WHO expert consultation (Lancet 2004; 363: 157–163); India: consensus statement for Asian Indians (JAPI 2009; 57: 163–170). Units: 1 in = 2.54 cm, 1 lb = 0.45359237 kg.
Questions
How is BMI calculated?
Weight in kilograms divided by height in metres squared. 65 kg at 1.70 m: 65 ÷ 1.70² = 22.5. In pounds and inches: 703 × pounds ÷ inches².
What is a healthy BMI?
For adults, 18.5 to 24.9. Below 18.5 is underweight, 25 to 29.9 overweight, and 30 or more obesity, in three classes (WHO and CDC).
Is BMI different for women and men?
No. Adult BMI uses the same formula and the same ranges for women and men. Children's BMI is compared with children of the same sex and age.
Why does the calculator ask about family background?
Some groups have a higher risk of type 2 diabetes and heart disease at a lower BMI. NICE in the UK uses lower cut-offs for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background: overweight from 23 and obesity from 27.5. In India, doctors use 23 and 25. The question is optional, and your answer isn't saved or sent.
How is a child's BMI different?
A child's BMI changes as they grow, so it's compared with other children of the same age and sex as a percentile, using the CDC growth charts. Below the 5th percentile is underweight, the 85th to below the 95th overweight, and the 95th or above obesity.
What does my healthy weight range mean?
It's the weights that give a BMI from 18.5 to 24.9 at your height (18.5 to 22.9 with the lower cut-offs). It's a broad guide, not a target; talk to a doctor before trying to change your weight.
What is waist-to-height ratio?
Your waist divided by your height. NICE suggests keeping your waist to less than half your height (a ratio under 0.5), because fat around the middle carries more risk.
When is BMI not accurate?
It doesn't tell fat from muscle, so very muscular people can show as overweight. It's less reliable for people over 65, after an amputation, and it isn't used in pregnancy.
Why is my range 0.1 kg different from another site?
We show exactly the weights this page labels healthy. A weight that rounds to a BMI of 24.9 counts as healthy here, so the range can end 0.1 kg higher than 24.9 × height².
Are my measurements sent anywhere?
No. Everything is worked out in your browser. A shared link carries the measurements after a #, a part of the link that browsers don't send to servers, and never your family background.