Clinical BMI Calculator
Fuel & FastingRESULT IN BMI · KG/M²
Editorial & evidence standards
Built on WHO anthropometry standards
WHO Technical Report Series on the use and interpretation of anthropometry (1995), the NHLBI/WHO adult cut-offs, and Nuttall's critical review of BMI as a health measure (2015) · independent RD/MD review pending
Updated June 2026
Inputs
Biological sex
Unit system
32 yrs
78 kg
178 cm
Activity level
Goal
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Shown for convenience only — informational, not medical advice or an endorsement.
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Build your profile Methodology & Sources · E-E-A-T Cited
How the BMI calculator works
Built on peer-reviewed research and independently cross-checked against the published literature — so the number you get is defensible, not a guess.
Key takeaways
- One ratio, two numbers — BMI needs only your height and weight: weight in kilograms divided by height in metres squared (or 703 × lb ÷ in² in imperial units).
- Healthy sits at 18.5–24.9 — below 18.5 is underweight, 25.0–29.9 is overweight and 30 or more is obese, following the WHO adult classification.
- It is a screen, not a diagnosis — BMI flags whether your weight is worth a closer look; it cannot tell you how much of that weight is fat versus muscle.
- Muscle reads as 'overweight' — very muscular athletes are often pushed into the overweight band despite low body fat, which is a known limitation, not an error.
- Waist and composition add context — pairing BMI with a waist measurement or a body-fat estimate gives a far more honest picture of metabolic risk.
01
What is BMI?
Body Mass Index, or BMI, is the single most widely used screening number in weight and nutrition. It compares your weight to your height using one simple ratio, and the result places you into one of four broad bands — underweight, healthy, overweight or obese. Its appeal is its simplicity: it needs no scale beyond an ordinary one, no tape measure and no lab test, which is exactly why doctors, public-health bodies and insurers have relied on it for decades.
What BMI is really good at is describing populations. Across thousands of people, a higher average BMI tracks reliably with higher rates of weight-related conditions, which makes it a useful first filter. For any single person, though, it is only a starting point — a prompt to look closer, never the final word on your health.
02
How it is calculated
The formula is weight in kilograms divided by height in metres squared. If you think in imperial units, the equivalent is 703 multiplied by your weight in pounds, divided by your height in inches squared. Clinarix always computes from metric internally and simply converts your entries, so the answer is identical whichever units you choose. A person weighing 70 kg at 1.75 m, for example, has a BMI of 70 ÷ (1.75 × 1.75) ≈ 22.9 — comfortably inside the healthy band.
Your result is then read against the World Health Organization's adult cut-offs: under 18.5 is underweight, 18.5 to 24.9 is the healthy range, 25.0 to 29.9 is overweight, and 30 or above is classed as obese. These thresholds are the same ones used in most national clinical guidelines, which is why the number on a hospital chart will match the number here. From your height the calculator also works backwards to show the actual weight range that would keep you inside the healthy band.
03
How to use your result
Treat your BMI as a conversation-starter rather than a verdict. If it lands inside the healthy range, that is reassuring but not a guarantee — composition and waist size still matter. If it falls into the overweight or obese bands, that is a reasonable cue to look at the fuller picture: how much of that weight is muscle, where the weight is carried, and how the trend has moved over months rather than days. A BMI a point or two outside the lines, held steady, is far less informative than a clear direction of travel over time.
Because BMI is built only from height and weight, it pairs naturally with the rest of your Clinarix profile. Use it alongside your TDEE and protein targets to plan a sustainable rate of change, and re-check it whenever your weight shifts meaningfully. Saved to your Wellness Snapshot, the number becomes a trend line — and a trend is almost always more useful than any single reading.
Who should not rely on this estimate?
BMI assumes an 'average' body, so it misleads whenever your composition is unusual. Highly muscular people — strength athletes, sprinters, many manual workers — frequently score in the overweight or obese bands while carrying very little fat, because muscle is dense and BMI cannot tell muscle from fat. At the other end, older adults often lose muscle with age, so a 'healthy' BMI can mask too little lean mass and too much fat. For these groups a body-fat or lean-mass estimate is far more honest than BMI alone.
BMI is also not designed for several specific situations. It should not be used to assess children and teenagers, who are read against age- and sex-specific growth percentiles instead; it is not a meaningful measure during pregnancy, when weight gain is expected and healthy; and the standard cut-offs may underestimate metabolic risk in some Asian populations, where lower thresholds are sometimes applied. If any of these describe you, treat this number as background information only and speak with a clinician or registered dietitian who can interpret it in context.
Citations · peer-reviewed sources
- 1
WHO Expert Committee on Physical Status. Physical status: the use and interpretation of anthropometry. WHO Technical Report Series 854. Geneva: World Health Organization; 1995.
WHO Technical Report - 2
Nuttall FQ. Body Mass Index: Obesity, BMI, and Health — A Critical Review. Nutrition Today. 2015;50(3):117–128.
PMID — pending verification - 3
WHO Expert Consultation. Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. Lancet. 2004;363(9403):157–163.
PMID — pending verification
FAQ · AI-extractable answer block
Frequently asked questions
How do I calculate my BMI?
Divide your weight in kilograms by your height in metres squared. For example, 70 kg at 1.75 m is 70 ÷ (1.75 × 1.75) ≈ 22.9. In imperial units, multiply your weight in pounds by 703, then divide by your height in inches squared. This calculator does the conversion and the maths for you in either unit.
What is a healthy BMI range?
For adults, the WHO classes a BMI of 18.5 to 24.9 as healthy. Below 18.5 is underweight, 25.0 to 29.9 is overweight, and 30 or above is obese. From your height, the calculator also shows the actual weight range that would keep you inside the healthy band.
Is BMI accurate?
BMI is an accurate screen across large groups but a blunt tool for individuals. It reflects total weight, not body fat, so it can label a muscular athlete 'overweight' or miss low muscle mass in an older adult with a 'healthy' score. Pair it with a waist measurement or body-fat estimate for a clearer picture.
Does BMI work for athletes and muscular people?
Often not well. Muscle is denser than fat, so very muscular people frequently fall into the overweight or obese bands despite low body fat. This is a well-known limitation of BMI, not a calculation error — athletes are better served by a body-fat or lean-mass measurement.
What BMI is considered obese?
A BMI of 30 or above is classed as obese for adults, and 25.0 to 29.9 is overweight. Some guidelines further split obesity into class I (30–34.9), class II (35–39.9) and class III (40+). These are screening categories — a clinician interprets them alongside your wider health.
Is the BMI calculator free?
Yes — every Clinarix calculator is free. Pro ($9/mo) adds unlimited longitudinal trends, AI insights and detailed reports, but calculating your BMI and seeing your category is always free.
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Important: This calculator provides general educational estimates and is not medical advice, diagnosis, or treatment. It is not a substitute for assessment by a licensed clinician or registered dietitian. Consult a qualified professional before making changes to your diet or training, especially if you have a medical condition, are pregnant or breastfeeding.