BMI Calculator — Quick Reference
The BMI Calculator is an online tool that calculate your Body Mass Index (BMI) with metric or imperial units, see WHO category, healthy weight range, and personalised insights. Everything for the BMI Calculator is on this page: the interactive calculator, the formula, a worked example, step-by-step guidance, and frequently asked questions — no other pages required.
At a glance
- Main inputs
- Weight (kg or lb)
- Height (cm or ft/in)
- Main outputs
- BMI and WHO category
- Healthy weight range for your height
- Weight to gain or lose for normal range
- BMI Prime
Direct answers
What is the BMI Calculator?
The BMI Calculator is an online tool that calculate your Body Mass Index (BMI) with metric or imperial units, see WHO category, healthy weight range, and personalised insights.
What formula does the BMI Calculator use?
Body Mass Index (BMI) = weight in kilograms ÷ (height in metres)². For imperial units, convert pounds to kg and feet/inches to metres first. The result is a single number used to classify weight status for most adults.
How does the BMI Calculator work?
Choose metric or imperial, enter age, gender, weight, and height. We compute BMI, BMI Prime, Ponderal Index, WHO category, healthy weight band, an 8-zone visual gauge, comparison chart, and personalised wellness tips — with a link to build a full diet and workout plan.
Formula Used
The equation below is what this calculator applies. Variable definitions follow when symbols are used.
Equation
BMI = weight (kg) ÷ height (m)²
Worked Example: 70 kg, 175 cm — what is the BMI?
Sample inputs and the results this calculator produces for the scenario below.
Inputs
- Weight
- 70 kg
- Height
- 175 cm (1.75 m)
Results
- BMI
- 22.9
- Category
- Normal weight (WHO)
- Healthy range
- 56.7 – 76.3 kg
BMI = 70 ÷ (1.75 × 1.75) = 22.9, which falls in the WHO normal range. For this height, a healthy weight band is roughly 56.7 to 76.3 kg.
How BMI Calculator Works
Choose metric or imperial, enter age, gender, weight, and height. We compute BMI, BMI Prime, Ponderal Index, WHO category, healthy weight band, an 8-zone visual gauge, comparison chart, and personalised wellness tips — with a link to build a full diet and workout plan.
What to enter
Use the calculator above to set your amounts, rates, and tenure. Results update as you move sliders or type values — switch currency if you are planning in USD, INR, or another supported unit.
Step-by-step
- Open the BMI Calculator and enter your amounts, rates, and time period in the input fields.
- Review the results panel — totals update instantly when you change any value.
- Compare the worked example and formula below to verify the math matches your scenario.
- Read the FAQs for common edge cases, tax notes, and planning tips specific to this calculator.
BMI — Frequently Asked Questions
Each question is answered directly below. Expand any item for the full response.
How is BMI calculated?
Body Mass Index (BMI) = weight in kilograms ÷ (height in metres)². For imperial units, convert pounds to kg and feet/inches to metres first. The result is a single number used to classify weight status for most adults.
What is a healthy BMI for adults?
The World Health Organization (WHO) defines normal weight as BMI 18.5 to 24.9 for adults aged 20 and older. Below 18.5 is underweight, 25.0–29.9 is overweight, and 30.0 or above is obese. These cut-offs are population screening tools, not individual diagnoses.
What is BMI Prime?
BMI Prime is your BMI divided by 25 (the upper limit of the normal range). A value below 1.0 means you are below the overweight threshold; above 1.0 means you are at or above it. It is a simple ratio some people find easier to interpret than raw BMI.
When is BMI not accurate?
BMI does not distinguish muscle from fat, so athletes and very muscular people may be classified as overweight despite low body fat. It is also less reliable for older adults, pregnant women, and some ethnic groups. Waist circumference and clinical assessment can add context.
How much should I weigh for my height?
For a given height, the healthy weight band corresponds to BMI 18.5–24.9. This calculator shows that range in kg or lb, plus an ideal reference weight at BMI 22.5 (mid-normal). Individual targets should account for muscle, health conditions, and professional guidance.
What is ponderal index?
Ponderal index is weight ÷ height³ (with height in metres). Some researchers use it alongside BMI because it may scale differently for very tall or short people. A normal PI is around 11–15 kg/m³. It is still a screening metric, not a diagnosis.
Who invented BMI?
Belgian statistician Adolphe Quetelet devised the "Quetelet Index" in 1832 as a population tool. Physiologist Ancel Keys coined "Body Mass Index" in 1972, and the WHO adopted it for global obesity screening in 1995.
Why can BMI mislabel muscular people as overweight?
BMI only compares weight to height — it cannot tell muscle from fat. Arnold Schwarzenegger at his 1974 peak had a BMI around 33 ("obese") with roughly 4–5% body fat. Use BMI alongside waist circumference, body composition, or clinical assessment.
Does BMI differ by ethnicity?
Yes. South and East Asian populations often face higher metabolic risk at lower BMIs; some guidelines use overweight from BMI 23 for Asian groups. Japan uses ≥25 as obese versus WHO's ≥30 globally. Always interpret BMI in context.
Disclaimer
- This calculator gives you an estimate only. It is not a promise of exact results.
- This is general information, not personal financial, tax, or legal advice.
- You are responsible for your own decisions. Talk to a qualified professional when it matters.
- BMI and weight guidance are screening estimates only — not a medical diagnosis. Consult a healthcare professional for personal advice.