BMI Calculator
Calculate your Body Mass Index and see which category it falls in.
Results update as you type.
About this calculator
Body Mass Index (BMI) is a simple ratio of weight to height used as a general indicator of whether your weight is in a healthy range. The formula is your weight in kilograms divided by the square of your height in metres (kg/m²); in imperial units it is 703 × pounds ÷ inches². The result drops into one of four bands — underweight, healthy, overweight or obese. Switch between metric and imperial units as you prefer.
For example, someone 175 cm tall weighing 70 kg has a BMI of 70 ÷ 1.75² = 70 ÷ 3.06 = 22.9, which sits in the healthy range of 18.5 to 24.9. For that height, a healthy weight runs from about 57 kg to 76 kg. The calculator also shows BMI Prime — your BMI divided by 25 — so a value under 1.0 means you are within the healthy limit.
Use BMI as a quick, free screen to see roughly where your weight sits and to track changes over time. It is a population-level tool, not a diagnosis: it cannot tell muscle from fat, so pair it with body fat percentage or a waist measurement for a fuller picture.
Frequently asked questions
What is a healthy BMI?
A BMI between 18.5 and 24.9 is generally considered healthy. Below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is in the obese range.
Is BMI accurate for everyone?
No. BMI does not distinguish muscle from fat, so it can misclassify athletes and does not account for age, sex or body composition. Treat it as a rough guide.
How do I calculate BMI by hand?
Divide your weight in kilograms by your height in metres squared. For 70 kg at 1.75 m: 1.75 × 1.75 = 3.06, and 70 ÷ 3.06 = 22.9. In imperial units, multiply weight in pounds by 703 and divide by height in inches squared.
What is BMI Prime?
BMI Prime is your BMI divided by 25, the top of the healthy range. A value of 1.0 means you are exactly at the upper healthy limit; below 1.0 is within range and above 1.0 is over it. It shows how far you are from the threshold at a glance.
Is BMI different for men and women?
The BMI formula and the standard adult categories are the same for both. On average women carry more body fat at the same BMI, so the number is best read alongside other measures rather than compared directly between sexes.
Does BMI work for children?
Not with these adult cut-offs. For children and teens BMI is compared against age- and sex-specific percentile charts instead. The age field here only flags that — treat a child’s result as informational, not a category.
What is a healthy weight for my height?
Multiply 18.5 and 24.9 by your height in metres squared to get the bottom and top of the healthy range. The calculator does this for you and shows the range in your chosen units next to your result.
API — use this calculator from code
Call this calculator as a free JSON endpoint — no key required. Send the field values below as query parameters or JSON. Read the full API docs →
Endpoint
GET https://calculator.free/api/v1/bmi/curl
curl "https://calculator.free/api/v1/bmi/?units=metric&height=175&weight=70"JavaScript fetch()
const r = await fetch(
"https://calculator.free/api/v1/bmi/?" + new URLSearchParams({
"units": "metric",
"height": "175",
"weight": "70"
}));
const data = await r.json();
console.log(data.results);Results are estimates for general guidance only, not financial, medical or tax advice.