Detailed BMI & Body Metrics
Compare your BMI from the classic Quetelet formula and the Oxford-adjusted formula, calculated entirely on your device
Measurements
Two Ways to Calculate BMI
The classic Body Mass Index (BMI) divides mass by height squared. While universal, this 19th-century formula can distort estimates for unusually tall or short individuals by not scaling volumetrically.
Oxford alternative: Proposed by mathematician Nick Trefethen at Oxford University, the equation (1.3 × weight / height^2.5) scales weight with height differently. It aims to reduce the height bias of the classic formula; it is not a clinical standard.
Your Results
How to use this tool
- Choose Metric (cm / kg) or Imperial (in / lbs) with the toggle.
- Enter your height and weight; the result updates as you type.
- Compare the classic BMI (Quetelet) with the Oxford-adjusted value and read the reference weight range for your height.
- Use it as a general benchmark for adults only, and talk to a health professional about body composition.
Worked example
For an adult who is 175 cm tall and weighs 70 kg, the classic BMI is 70 ÷ 1.75² = 22.9. The Oxford formula (1.3 × weight ÷ height^2.5) gives 22.5, slightly lower because it corrects for the way taller bodies scale. The reference BMI band of 18.5–24.9 translates, for 175 cm, into a weight range of 56.7–76.3 kg, so 70 kg sits inside it. BMI cannot tell muscle from fat, so an athlete could land in the same band as a sedentary person.
Why this tool exists and where its numbers come from
BMI is the quickest way to place weight against height. The adult overweight (25) and obesity (30) cut-offs follow WHO; the alternative formula is a mathematician's proposal, not a clinical standard, and BMI says nothing about body composition or individual health.
Sources
For the full method, see the Methodology section just below.
Methodology
The standard BMI categories follow the adult cut-offs of the World Health Organization (WHO). The alternative formula comes from a 2013 proposal by Oxford mathematician Nick Trefethen; it is a mathematical suggestion, not a clinically adopted standard.
What the 18.5–24.9 band means at six heights
Reference weight range (BMI 18.5 to 24.9) exactly as the tool calculates it, plus the Oxford value that those same two weights would produce:
| Height | Reference weight range | Oxford value at those weights |
|---|---|---|
| 150 cm | 41.6 – 56.0 kg | 19.6 – 26.4 |
| 160 cm | 47.4 – 63.7 kg | 19.0 – 25.6 |
| 170 cm | 53.5 – 72.0 kg | 18.4 – 24.8 |
| 180 cm | 59.9 – 80.7 kg | 17.9 – 24.1 |
| 190 cm | 66.8 – 89.9 kg | 17.4 – 23.5 |
| 200 cm | 74.0 – 99.6 kg | 17.0 – 22.9 |
How to read it: the band is not a fixed number of kilos; it is about 14 kg wide at 150 cm and about 26 kg wide at 200 cm, because weight scales with height squared. The Oxford column shows why that formula exists: it gives taller people a lower number and shorter people a higher one for the same classic BMI, with the two formulas agreeing at roughly 169 cm.
This is a general adult benchmark only. BMI does not separate muscle from fat, does not apply to children, teenagers or pregnancy, and the Oxford figure is a mathematical proposal, not a clinical category. It is not medical advice.
Tools for Measuring at Home
A scale, a body tape measure and a skinfold caliper for taking your own measurements at home
Smart bioimpedance body composition scale
A bathroom scale that also gives bioimpedance estimates and syncs with an app, according to the listing. Body-fat figures from such scales are estimates.
Retractable body measuring tape
A retractable body measuring tape with a pin lock, according to the listing, for measuring the waist the same way each time.
Skinfold caliper with measurement chart
A skinfold caliper with a measurement chart, according to the listing. Readings depend a lot on technique, so treat them as estimates.
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Frequently asked questions
What is the difference between Standard BMI and Oxford New BMI? ▼
Standard BMI divides mass by height squared, which can unfairly assign higher numbers to taller individuals and lower numbers to shorter individuals. The Oxford equation uses an exponent of 2.5 to better reflect the three-dimensional geometric scaling of the human frame.
Why does this tool not track muscle vs. fat tissue? ▼
BMI equations only evaluate gross mass relative to height. High-density lean muscle tissue weighs more by volume than adipose tissue, meaning athletic individuals may show an elevated index without having excess body fat.
What do Reference Range and Distance to Range mean? ▼
The Reference Range shows the weight span that falls inside the standard 18.5-24.9 bracket at your entered height. Distance to Range is the difference between your current weight and the nearest edge of that span. It is a mathematical comparison, not a personal goal or health recommendation.
How do the two BMI values compare for a real example? ▼
For 70 kg at 1.75 m, standard BMI is 70 / 1.75² = 22.9 and the Oxford value is 1.3 × 70 / 1.75^2.5 = 22.5. The reference weight range for that height is 18.5 × 1.75² to 24.9 × 1.75², or 56.7 to 76.3 kg. The factor 1.3 is chosen so both formulas agree at a height of about 1.69 m, because 1.69 to the power 0.5 equals 1.3. Above that height the Oxford figure is lower than the standard one, and below it the figure is higher. Pounds and inches are converted to kg and meters first.
Who should not rely on these BMI categories? ▼
The WHO cut-offs apply to adults. Children and teenagers are assessed with BMI-for-age growth charts, and pregnancy, very high muscle mass, older age and loss of muscle all distort the number. The WHO expert consultation published in The Lancet in 2004 also noted that health risks in some Asian populations appear at lower BMI values than the standard cut-offs. BMI is a screening number, not a diagnosis. Talk to a doctor or registered dietitian before making health decisions based on it.