BMI Calculator
Calculate body mass index with metric or imperial units and see the standard adult BMI category.
🔒 Runs entirely in your browser — nothing is uploadedHow BMI is calculated
Body mass index, or BMI, compares weight with height using a simple formula. In metric units, the formula is BMI = weight(kg) ÷ height(m)². A person who weighs 70 kg and is 1.75 m tall has a BMI of 70 ÷ 1.75², which is about 22.9. In imperial units, the same idea is adjusted for pounds and inches: BMI = weight(lb) ÷ height(in)² × 703. The multiplier converts the imperial measurement into the same index scale used by the metric formula.
This page supports both systems so you can use whichever measurements you already know. The calculation happens immediately in the browser, and the formula line shows the converted math so you can spot obvious entry mistakes such as typing inches into the centimeter field.
Understanding BMI categories
Adult BMI categories are commonly grouped as underweight below 18.5, normal weight from 18.5 to 24.9, overweight from 25 to 29.9, and obesity at 30 or higher. These ranges are useful for population-level screening and quick conversations about weight status. They are not a full health assessment. Athletes with high muscle mass may have a high BMI without excess body fat, while older adults or people with certain conditions may need a more nuanced interpretation.
Use BMI as a starting point
Treat BMI as one input, not a verdict. Waist measurement, blood pressure, cholesterol, fitness, medication, age and medical history can all matter. If the result concerns you or you are using it for a health decision, speak with a qualified clinician. Calc Tools does not upload your measurements, does not create a profile and does not provide medical advice. It simply applies the standard formula locally so you can get a quick, private estimate.
Worked example and common mistakes
In imperial units, a person who weighs 154 lb and is 69 in tall has a BMI of 154 ÷ 69² × 703 = 154 ÷ 4,761 × 703 ≈ 22.7, which falls in the normal weight range. A result of 25 or above is classed as overweight, and 30 or above as obesity.
Most wrong results come from unit slips. Entering height in meters in the centimeter field, or feet in the inch field, produces an absurd index, so glance at the formula line under the result. The calculator has no age or sex input, which means it gives the standard adult figure only. It is not designed for children and teenagers, whose BMI is interpreted against age-specific percentile charts.
How to use
- Pick unitsChoose metric for kilograms and centimeters or imperial for pounds and inches.
- Enter measurementsType weight and height. Results update automatically as the values change.
- Review categoryRead the BMI value with the standard adult BMI category shown below it.