bmi calculator — the complete guide
This guide covers the BMI Calculator end to end: what it does, what each field means, the formula behind it, worked examples, and the limits of the result. If you only need the answer, enter your numbers and read the headline. If you want to trust the answer, read on.
The inputs, in order, are the numbers the formula needs — no more, no less. Enter them in the units shown beside each field, and check the units before you move on: a unit slip is the single most common cause of a wrong result with any calculator.
Worked example: 70 kg at 170 cm: BMI = 70 ÷ 1.70² = 24.22, which sits in the healthy band of 18.5 to 24.9. The formula behind that example is: BMI = weight in kilograms ÷ (height in metres)². Run those numbers through the calculator and confirm the result matches. Then try your own numbers, one field at a time, so you can see which input moves the answer most.
The limits: BMI is an informational screening number, not a medical diagnosis. It does not distinguish muscle from fat, so treat it as a starting point, not a verdict. Within those limits, the calculator is exact arithmetic on the inputs you gave it. Outside them, it is still exact arithmetic — but on a question you did not mean to ask.
Frequently asked questions
What does this guide cover that the tool page does not?
The same calculation, explained in full: every field, the formula, worked examples, common mistakes, and the limits of the result.
Where do I find the tool itself?
Through the button at the end of this guide, or from the site’s tool list. The guide and the tool use the same formula and the same worked example.
Is the result a promise or a guarantee?
Neither. It is arithmetic on the inputs you entered. Real outcomes vary with rates, prices and circumstances the calculator cannot see.
More guides on the BMI Calculator
- How to use the BMI Calculator — step by step
- BMI Calculator explained with worked examples
- BMI Calculator formula — how it actually works
- BMI Calculator for beginners — start here
- Common mistakes people make with the BMI Calculator
- BMI Calculator vs doing it by hand — which is faster?
- How to get an accurate result from the BMI Calculator
- BMI Calculator for students — with examples
- BMI Calculator for homeowners and DIYers
Enter your height and weight to see your BMI and which band it falls in.