BMI Calculator — Body Mass Index

What this BMI calculator does

This English-language body mass index BMI calculator takes your height and weight — in either metric (cm/kg) or imperial (in/lb) — and returns your BMI score alongside the WHO healthy diet classification ranges for adults: underweight, normal weight, overweight, and obese. The WHO defines overweight as BMI ≥ 25 and obesity as BMI ≥ 30, thresholds used by clinicians and public-health researchers worldwide. The tool is honest about what this body weight index number means: it is a population-level screening statistic, not a medical verdict. Results appear next to the full range chart so you can place your score in context rather than read a single label in isolation. 100% client-side — your data never leaves your browser. No uploads, no tracking, no server logs.

Features

Metric and imperial input. Switch between centimeters/kilograms and inches/pounds. The imperial formula applies the standard 703 multiplier — (lbs / inches**2) * 703 — so results match clinical reference tables exactly.
Instant WHO classification. Your category — underweight, normal, overweight, or obese — is highlighted as soon as you enter values, with the full BMI index chart shown alongside for reference.
Honest limitations notice. The result panel explains that BMI doesn't capture body composition, fat distribution, or metabolic health, and that athletes with high muscle mass can score in the overweight range despite low body fat.
Ethnicity context. A note flags that WHO cutoffs are derived from white European populations; some guidelines recommend lower thresholds for certain Asian populations — a distinction worth discussing with a clinician.
No account, no data retention. All computation runs in your browser using weightKg / (heightM ** 2). Nothing is stored, logged, or transmitted. Works fully offline once the page loads.
Paired health tools. For a fuller picture of energy needs, the [TDEE calculator](/en/tdee-calculator/) estimates your total daily energy expenditure, and the [Macro Calculator](/en/macro-calculator/) breaks that into protein, fat, and carb targets.

How to use the BMI calculator

Enter two values and the result appears immediately — no button press needed.

Choose your unit system. Select Metric (cm, kg) or Imperial (in, lb) using the toggle at the top of the calculator.
Enter your height. Type your height in the appropriate field. For metric, use centimeters (e.g. 175). For imperial, use total inches (e.g. 69 for 5 ft 9 in).
Enter your weight. Type your weight in kilograms or pounds. The calculator applies weightKg / (heightM ** 2) for metric or (lbs / inches**2) * 703 for imperial.
Read your result. Your BMI score and WHO category appear instantly. The range table below the result shows where your score sits among all four classifications.
Check the context note. Read the limitations panel before drawing conclusions — especially if you carry significant muscle mass or have a heritage for which standard cutoffs may not apply.

Common use cases

Personal health screening. Use your BMI score as one data point alongside blood pressure, fasting glucose, and waist circumference — not as a standalone diagnosis.
Tracking weight changes over time. Recalculate your body mass ratio periodically to see whether changes in weight are moving you toward or away from the normal range relative to your height.
Medical and insurance intake forms. Many forms ask for your BMI or corporal mass index value. This tool gives you the number instantly, so you're not estimating or converting units under pressure in a waiting room.
Health education. Teachers and coaches explaining body weight index concepts can walk through the WHO ranges on-screen in real time, showing students or athletes how height interacts with weight in the calculation.
Pre-appointment research. Knowing your BMI before a check-up in Austin, Seattle, or anywhere else means you arrive with context, ready to ask more specific questions about what the number does — and doesn't — tell your doctor.

Frequently asked questions

Is my data sent to any server when I use this calculator?

No. The entire calculation runs in your browser with JavaScript. No value you enter is transmitted, stored, or logged. The page works offline after it first loads, and there are no cookies tied to your inputs.

Can I reach a normal BMI after years of being in the obese range?

Yes — the calculator has no memory of past results, so every session reflects your current numbers. Sustained weight loss that lowers your BMI below 25 will show as normal weight. The body mass index is a ratio, so both reducing weight and accounting for height matter. It is not a ceiling — people do move categories.

Why does the imperial formula multiply by 703 instead of a round number?

BMI was defined in metric (kg/m²). Converting pounds and inches to those units algebraically produces the factor 703.07, rounded to 703. Using 705 — a common shortcut — introduces a small but real error. This calculator uses 703 to match the standard clinical definition.

Does BMI apply the same way to athletes and highly muscular people?

Not always. BMI measures the ratio of mass to height squared and cannot distinguish fat from muscle. A bodybuilder or professional athlete may score in the overweight or obese range despite having very low body fat. The limitations notice in the result panel flags this directly. For body-composition detail, a DEXA scan or skinfold measurement is more informative.

Are the WHO cutoffs the same for all ethnicities?

The standard WHO thresholds — overweight ≥ 25, obese ≥ 30 — were derived primarily from studies on white European populations. Research has shown that equivalent metabolic risk can appear at lower BMI values in some East and South Asian populations. The WHO healthy diet fact sheet and related WHO reports discuss these considerations. This calculator shows the universal adult thresholds; your clinician can advise on whether an adjusted cutoff applies to you.

How is BMI different from body fat percentage or TDEE?

BMI is a simple height-to-weight ratio — fast to compute but blind to body composition. Body fat percentage tells you how much of your mass is adipose tissue, which requires a separate measurement. TDEE (total daily energy expenditure) is about how many calories you burn in a day, which has nothing to do with your current weight classification. If you need TDEE alongside your BMI, the [TDEE calculator](/en/tdee-calculator/) is a quick next step.