BMI Calculator
BMI calculator works out BMI and Category from Units, Weight and Extra pounds. The default figures on this page give BMI of 24.22 kg/m^2; change any entry and the result, the working and the sources update together.
Your figures
Updates as you typeHow this is worked out
5 steps
- Weight = 70.0 kg = 70 kg
- Height = 170 cm = 1.7 m, so height squared = 2.89 m^2
- BMI = 70 / 2.89 = 24.22 kg/m^2
- WHO international classification: 24.22 falls in "Normal range". WHO adult cut-points: under 18.5 underweight, 18.5-24.9 normal, 25.0-29.9 overweight, 30.0 and above obese.
- Healthy weight for this height = 18.5 to 24.9 x 2.89 = 53.47 to 71.96 kg
Its 4 worked examples are re-run on every release, last on 15 September 2026. What changed
Sources and references
5 sources
Keep this result
Save it, change one figure, then compare the two
The calculation stays free. Save this scenario, adjust one assumption, save that too, and put them side by side to see exactly what the change costs you. A free account keeps 5 scenarios and 2 comparisons; Personal makes both unlimited and adds exports and private links. Nothing is saved unless you press Save.
What the bmi calculator calculates
Body mass index from height and weight, with the WHO, CDC, NHS or Asian classification band and the healthy weight range for that height.
How to use this bmi calculator
Enter Units, Weight, Extra pounds and Height. BMI updates as you type, and “Use a worked example” loads checked figures you can adjust. Change one figure at a time to see what drives the result.
How the result is worked out
Open “How this is worked out” beside the result for the step-by-step calculation behind BMI, Category and Healthy BMI range.
The method follows World Health Organization - Body mass index (BMI) and the international classification of adult underweight, overweight and obesity, CDC - Adult BMI Categories, NHS - Calculate your body mass index (BMI) for adults, WHO Expert Consultation - Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies and NIST SP 811 - exact definitions of the international pound (0.45359237 kg) and inch (0.0254 m) used for the US and UK unit paths.
70 kg at 175 cm (WHO) example
With Units: metric, Weight: 70, Height: 175, Classification table: who, the calculator returns BMI: 22.86, Category: Normal range, Healthy weight, lower: 56.66. This example is checked against an independent source in the test suite.
What you can compare
Change one input at a time to see how it affects BMI, Category and Healthy BMI range. The inputs you can vary are Units, Weight, Extra pounds, Height, Height (feet) and Height (inches).
Understanding BMI, Category and Healthy BMI range
BMI is a population screening measure, not a diagnosis. It does not distinguish muscle from fat and is not valid for children and teenagers, during pregnancy, or for highly muscular people. Discuss any weight concern with a clinician.
Results are general information, not financial, tax, legal, medical or engineering advice. Check any decision that matters with a qualified professional.
See something wrong? Report a problem with this calculator
Frequently asked questions
What information do I need for the bmi calculator?
You need Units, Weight, Extra pounds, Height, Height (feet), Height (inches), Classification table and Age. The page opens with default figures that give BMI of 24.22 kg/m^2, so you can see the scale before entering your own.
What does this bmi calculator show?
It shows BMI, Category, Healthy BMI range, Healthy weight, lower, Healthy weight, upper, Weight to lose (+) or gain (-) to reach the healthy range, BMI prime (BMI / 25) and Ponderal index, with the working and any warnings for your entries.
Can I check how the bmi calculator result was calculated?
Yes. The “How this is worked out” section shows the calculation steps, and the sources section identifies the references used for the method.