How to calculate BMI
Body Mass Index is weight divided by height squared. In metric units:
BMI = weight (kg) ÷ height (m)²
Example: 70 kg and 1.75 m → 70 ÷ 3.0625 ≈ 22.9. In pounds and inches the same relationship uses a 703 multiplier. The tool does that conversion when you switch units.
The original index is often traced to Adolphe Quetelet. Modern adult cut-offs used on this page follow the widely published World Health Organization bands for adults.
Adult categories we display
- Underweight: BMI under 18.5
- Healthy weight: 18.5 to 24.9
- Overweight: 25.0 to 29.9
- Obesity range: 30.0 and above
Some regional guidelines use lower overweight thresholds for people of Asian ancestry. This tool does not silently change the cut-off. If that applies to you, ask a clinician which chart they use.
What to do with a result
If your number sits in the healthy band, the useful next step is usually food quality and movement you can keep — not a new product. Read anti-inflammatory foods.
If the number is high or low, treat it as a flag. Waist, sleep, medicines, and muscle mass can all change the story. The calorie calculator estimates energy need. The meal framework is for building plates without crash rules.
Frequently asked about this tool
Why do I not enter age on the BMI form?
Standard adult BMI does not use age. Age matters more for body-fat estimates and calorie need — use those tools if you have it.
Can athletes trust this number?
Often no. High muscle raises BMI. Read limitations.
Is a BMI over 25 automatically unhealthy?
No. It is a category on a chart. Blood pressure, glucose, fitness, and waist-to-height ratio add context.
References for readers: WHO adult BMI classification; CDC healthy-weight pages. We summarize, we do not host those agencies.
Worked examples
80 kg at 1.70 m: 80 ÷ 2.89 ≈ 27.7, in the overweight band on WHO-style adult charts. 60 kg at 1.70 m: 60 ÷ 2.89 ≈ 20.8, in the healthy band. Same height, different mass, different category. Neither example is a diagnosis.
In US units, 154 lb at 67 in: BMI = 703 × 154 ÷ (67 × 67) ≈ 24.1. Switch the form to imperial and you should land near that figure. Small differences come from rounding.
Height, ageing, and the band this tool prints
The healthy-weight range under the result reverses the 18.5 and 24.9 cut-offs for your height. It is a map key. Some adults function well slightly outside it. Some adults inside it still need bloodwork. Use the range as a planning window, then read where BMI falls short.
People lose a little height in later decades. Measuring against a wall once a year keeps the denominator honest. Do not use a height from an old passport if you know you have lost centimetres.
After you have a number
If you care about energy, go to the calorie calculator. If you care about plates, go to the meal framework and foods list. If the actual problem is walking or stairs, use the knee or back guides. Split the questions so this page does not have to pretend it is a clinic.
The form does not send height or weight to our server. See privacy and the disclaimer.
Athletes, people on steroid medicines, and anyone with oedema should treat the result as especially noisy. Fluid is mass. Muscle is mass. The formula cannot split them. Take the number to a person who can look at you, not just at a ratio. For food after the appointment, the weeknight dinners stay available.