BMI Calculator formula — how it actually works
The whole calculator is one formula: BMI = weight in kilograms ÷ (height in metres)². Every field on the page feeds exactly one part of that formula, and nothing else is going on behind the scenes. Knowing that makes the result checkable, not mysterious.
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. You can follow that example by hand with a pocket calculator. If your hand calculation gives a different answer, compare each input one by one — the formula rarely goes wrong, but a mistyped input goes wrong often.
A useful hand check is to try a round-number version first. Round numbers make the arithmetic easy to follow, and they confirm you understand the method before you trust it with your real figures. Once the method checks out, the real figures are just a second run.
One limit of the formula: 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. The formula is correct for what it covers, and silent about what it does not. Read the result with that limit in mind.
Frequently asked questions
What does each symbol in the formula mean?
Each symbol is one field on the tool page, in the same order. The formula page on the tool itself names them, and the worked example shows them substituted with real numbers.
Can I check the result by hand?
Yes, and you should try it once with round numbers. The worked example on the tool page is designed to be checkable with a pocket calculator.
Does the formula include tax, fees or other charges?
Only what the formula says. Anything outside it — tax, fees, charges, or real-world variation — sits outside the result, so read the result with that in mind.
More guides on the BMI Calculator
- How to use the BMI Calculator — step by step
- BMI Calculator explained with worked examples
- BMI Calculator for beginners — start here
- Common mistakes people make with the BMI Calculator
- BMI Calculator vs doing it by hand — which is faster?
- bmi calculator — the complete guide
- 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.