BMI calculator.
Use this calculator to estimate your Body Mass Index (BMI) using metric or imperial units. You’ll also find worked examples, health interpretation ranges, common pitfalls, and answers to frequently asked questions.
Calculate your BMI
BMI is a population screening tool, not a diagnosis. See “Limitations” below.
Interpreting your result
Enter your details above to see a personalised interpretation here. We’ll explain what your number means and how it relates to general health ranges.
Frequently asked questions
Is BMI accurate for runners?
It’s a useful high‑level screen, but trained runners with higher muscle mass may appear “overweight” by BMI despite low body‑fat. Track trends over time and consider waist measures and body‑fat % for context.
What BMI range is considered healthy?
For most adults, a BMI of 18.5–24.9 is considered within the healthy range. For personalised advice, speak to a qualified health professional.
Why do athletes often have higher BMI?
Because BMI uses weight without separating lean mass from fat mass. Muscle is denser than fat, so athletic builds can produce higher BMI values.
Should I change my training based on BMI alone?
No. Combine BMI with performance metrics (pace, heart‑rate zones), recovery, nutrition, and professional guidance.
BMI formula deep dive
Body Mass Index is a simple ratio that divides body mass by the square of stature. Because height can be measured in metres or inches (and mass in kilograms or pounds), we support both formulations and apply conversions under the hood.
| Formula | Expression | When it’s ideal |
|---|---|---|
| Metric BMI | BMI = weight(kg) ÷ height(m)2 | When your measurements are already in kilograms and centimetres. This is the base definition endorsed by WHO. |
| Imperial BMI | BMI = 703 × weight(lb) ÷ height(in)2 | When you track in pounds and inches. The constant 703 converts pounds/inches to the metric ratio. |
Internally we convert centimetres to metres (divide by 100) before squaring, and combine feet and inches into a total inch value. Results are rounded to one decimal place for readability. Health ranges (underweight, healthy, overweight, obesity) are applied after the BMI value is computed.
Metric vs. imperial trade‑offs
- Metric (kg/m²) — plus: direct use of the original formula, no extra constants, less rounding error. Minus: may require converting if you weigh in pounds.
- Imperial (703 × lb/in²) — plus: easy mental math for users of imperial units, compatible with US medical charts. Minus: relies on the 703 scaling factor and small rounding differences compound when heights are estimated.
Remember that BMI estimates body fatness across populations, not individual health. For muscular or smaller-framed athletes, combine BMI with waist circumference, body-fat percentage, and professional assessment.