Health

BMI Calculator

Free BMI calculator. Enter height and weight in metric or imperial units to find your Body Mass Index and category.

YOUR WORKSPACEFree to use. No sign-up.

Units

Height (cm)

Weight (kg)

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Enter your height and weight above.

Deep dive guides

A LITTLE CONTEXT · 3 MIN READThe BMI Formula Explained

All 10 related guides

The BMI Formula Explained — What BMI is, the exact metric and imperial formulas, the category ranges, and the known limits of BMI as a health measure.
How Body Fat Is Measured — What body fat percentage means, how the US Navy tape method estimates it, BMI compared, how accurate each method is, and healthy ranges.
How Body Surface Area Is Calculated — BSA from height and weight: the Mosteller formula, Du Bois and its rivals, worked examples, and why medicine doses drugs per square meter of skin.
Waist-to-Height Ratio: The Measurement BMI Misses — Keep your waist under half your height: why WHtR sees the visceral-fat risk BMI is blind to, how to measure, and how it compares to waist-to-hip ratio.
How Much Water You Actually Need — Beyond eight glasses: the 35 ml per kg body-weight baseline, how exercise and climate change your target, what counts toward it, and the overhydration caveat.
Ideal Weight: Why Every Formula Disagrees — Devine, Robinson, Hamwi, and Miller ideal weight formulas compared: why the same height gets four answers, what they ignore, and the numbers that screen better.
Shoe Size Systems Explained — Foot length, lasts and the US, UK and EU scales — why no shoe size chart is universal and how to convert without getting burned.
Puppy Growth Curves: Predicting Adult Weight Before It Happens — Why breed size changes the growth curve, how percent-of-adult-weight tables work, and why any single projection deserves a range.
From BMI to a Calorie Target — The chain behind one readout: the BMI screen, a Mifflin-St Jeor BMR, an activity multiplier, and the goal adjustment that lands on daily calories.
Pregnancy Weight Gain: IOM Ranges and the Weekly Curve — IOM pregnancy weight-gain ranges by pre-pregnancy BMI, the flat first trimester, weekly rates, twin targets, and the running total by week.

How bmi calculator works

Body Mass Index (BMI) is a number derived from your height and weight that estimates whether your weight is in a healthy range for your height. The formula is the same worldwide: weight divided by the square of height. Metric units use kilograms and metres; imperial units use pounds and inches with a conversion factor of 703.

This calculator supports both unit systems. In metric mode you enter height in centimetres and weight in kilograms. In imperial mode you can enter height either as total inches or as feet and inches, and weight in pounds. The result is rounded to one decimal place and paired with the standard WHO category: underweight, normal, overweight, or obese.

BMI is a screening tool, not a diagnosis. It doesn't distinguish between muscle and fat, so very muscular people can register as overweight without being unhealthy. Use it as a starting point and consult a healthcare professional for personal advice. For most adults, a BMI between 18.5 and 24.9 is considered a healthy range.

Frequently asked questions

What is a healthy BMI?

For most adults, a BMI between 18.5 and 24.9 is considered a healthy weight. Below 18.5 is classified as underweight, 25–29.9 as overweight, and 30 or above as obese. These ranges are based on World Health Organization guidance.

How is BMI calculated?

BMI equals weight in kilograms divided by height in metres squared (kg/m²). For imperial units, the formula is 703 × weight in pounds ÷ height in inches squared. The calculator applies the correct formula based on your selected units.

Is BMI accurate for everyone?

BMI is a useful screening measure but has limits. It doesn't account for muscle mass, bone density, or fat distribution, so athletes and older adults may get misleading results. Treat it as a starting point, not a definitive health measure.

Can I use feet and inches?

Yes. Switch the units dropdown to Imperial and use the feet and inches fields. The calculator converts them to total inches before applying the imperial BMI formula.

BMI Calculator

Deep dive guides

How bmi calculator works

Frequently asked questions

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