What BMI Calculator helps you do
Calculate Body Mass Index from a height and weight in metric or imperial units. BMI is a simple ratio used as a rough screening measure, not a diagnosis. The page shows one decimal place and labels the result as underweight, normal weight, overweight or obese using the standard bands.
The calculation runs in your browser. Your height and weight are not uploaded or stored.
How it works
These are everyday arithmetic calculators: a percentage, a tip split, a body-mass index and a loan installment. Each one applies a fixed formula to the numbers you type and updates as you edit; nothing is looked up and nothing is sent to a server. The display rounds to a couple of decimals, but the calculation itself keeps full precision until the final formatting step. Because the formulas are simple, the assumptions around them matter more than the arithmetic: whether a tip is calculated before or after tax, whether a BMI scale fits the person, and whether a loan uses reducing balance or a flat markup.
How to use BMI Calculator
- Choose metric or imperial units.
- Enter the height and weight in those units.
- Read the BMI value and its category.
- Treat the category as a screening band, not a diagnosis.
When to use it
- Get a quick BMI figure from height and weight.
- Compare metric and imperial inputs for the same person.
- Track changes over time using the same measure.
- Sanity-check a BMI quoted in a document.
- See which standard band a value falls into.
- Prepare an informational note for a fitness plan.
When not to use it
- Do not use it to diagnose or rule out a health condition.
- Do not apply adult bands to children or pregnant people.
- Do not assume it reflects body fat, muscle or fitness.
Example
A weight of 70 kilograms at a height of 175 centimeters gives a BMI of about 22.9, which falls in the normal-weight band. The same person entered as 154 pounds and 69 inches gives the same result after conversion. A BMI of 18.4 is underweight by the bands, while 25.0 crosses into overweight.
What you can do with BMI Calculator
- Calculate BMI from kilograms and centimeters.
- Calculate BMI from pounds and inches.
- Show one decimal place.
- Label the standard BMI category.
- Update as you change the inputs.
- Run the calculation locally in the browser.
Example: check the assumption, not just the arithmetic
Confirm the units before trusting the number. Kilograms versus pounds and centimeters versus inches change a BMI completely.
Check what the percentage is taken from. A percentage of the bill, of the pre-tax total and of the post-tax total are three different amounts.
Round only at the end. Rounding a tip or an installment early can shift the total by more than a cent.
Read the result in context. A BMI category is a screening band, not a diagnosis, and a monthly payment says nothing about the total cost.
Do not treat a general-purpose calculator as medical, tax or financial advice.
Decide how the result should be rounded for its use. A tip may round up to the next note, while an installment is usually fixed by the lender's own rounding rule.
Check the direction of a change. A rise from A to B and a fall from B to A are different percentages, even though the amounts are the same.
What to know before you start
- BMI does not distinguish muscle from fat, so athletes can read as overweight.
- It is a screening measure and not a medical assessment; consult a professional for health advice.
- The adult bands do not apply to children, pregnancy or some medical conditions.
- It uses a single formula and does not account for age, sex or body composition.
Common mistakes
- Entering pounds while the units are set to metric.
- Entering height in meters when the metric field expects centimeters.
- Treating the category as a medical conclusion.
- Comparing a child's BMI with adult bands.
Troubleshooting
If the result is implausibly high or low, check the height unit first.
If the value does not change, one field may be empty or invalid.
If the category looks wrong, compare the exact value with the band boundaries.
If you need a clinical assessment, use a professional rather than this page.
Related standards and documentation
- The World Health Organization publishes the BMI classification bands used here.
- WHO growth standards cover children, which is why adult BMI bands do not apply to them.
- ISO 4217 defines currency codes, though these pages display a symbol rather than a full locale format.
- The standard annuity formula relates principal, monthly rate, payment and term for the EMI calculation.
- SI units define the kilogram and metre relationships behind the metric conversions.
- Check units first.
- Know the base amount.
- Round at the end.
- Context matters.