Rex says
BMI is a crude single number — it doesn't know if you lift, doesn't know your bone structure. Use it as a quick gut-check, not a verdict. If you're an athlete or very muscular, body fat % is the better read.
Try a scenario
Click to load — tweak from there.Inputs
Result
Your BMI
25.8
Category
Overweight
25.8 reads as overweight. Could mean fat, could mean muscle — body fat % tells you which.
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One click, a permanent link with your numbers baked in.
How to read your BMI
- 1Pick Metric or Imperial — your scale and tape measure decide.
- 2Type your weight (lb or kg) and height (in or cm).
- 3Watch the BMI number and category update live as you adjust.
- 4If you're muscular, also check the Body Fat calculator — BMI overcounts lean mass.
About this calculator
BMI is weight in kilograms divided by height in meters squared. Under 18.5 is underweight, 18.5–24.9 normal, 25–29.9 overweight, 30+ obese.
Worked example
Using the values the calculator loads with:
Inputs
- Units: Imperial (lb, in)
- Weight: 170
- Height: 68
Results
- Your BMI: 25.8
- Category: Overweight
What each field means
Inputs
- Units
- Pick the option that matches your situation — the maths changes per option. Choices: Metric (kg, cm), Imperial (lb, in).
- Weight
- The weight used in the calculation. Starts at 170 so you have a working example on load.
- Height
- The height used in the calculation. Starts at 68 so you have a working example on load.
Results
- Your BMI
- Returned as a decimal number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Category
- Returned as a plain value. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How does the bmi calculator work?
BMI is weight in kilograms divided by height in meters squared. Under 18.5 is underweight, 18.5–24.9 normal, 25–29.9 overweight, 30+ obese. The underlying maths is: BMI = kg / m².
What do I need to enter?
3 values: units, weight, and height. Each field starts with a sensible default, so you can change one number at a time and watch the result move.
What does the your bmi result mean?
It is returned as a decimal number and updates live as you edit the inputs, so you can compare two or three versions of a scenario in a few seconds.
Is this calculator free, and do I need an account?
Yes, it's free, and no account is required. Nothing you type is stored on our servers — the maths runs entirely in your browser.
How accurate is the result?
It applies the standard formula exactly, so the arithmetic is precise. Population formulas describe averages; individual bodies vary, especially at the extremes of height, age, or muscle mass.
Who is this tool for?
It's built for anyone tracking a health or training target and wanting the standard formula applied correctly, without a signup or an app.
Accuracy and limitations
- Population formulas describe averages; individual bodies vary, especially at the extremes of height, age, or muscle mass.
- Results do not account for medical conditions, medication, or pregnancy.
- Use this as a directional reference, not a diagnosis — talk to a clinician before acting on it.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). BMI Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/bmi
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/bmi" target="_blank" rel="noopener">BMI Calculator — RevenueLab</a> (2026).</p>
Source: [BMI Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/bmi) (2026).