Is BMI accurate for athletes and muscular people?

Not reliably. BMI only uses weight and height, so it can't tell muscle from fat. A muscular person can land in the "overweight" or "obese" range despite having low body fat. Body fat percentage or a DEXA scan gives a more accurate picture for very muscular people.

How do you calculate BMI using feet and inches?

The imperial formula is BMI = (weight in lbs × 703) ÷ (height in inches)². This calculator does that conversion automatically when you select "Imperial" — just enter feet and inches separately.

What BMI categories does the WHO define for adults?

Underweight (below 18.5), normal weight (18.5–24.9), overweight (25.0–29.9), and three classes of obesity (30.0–34.9, 35.0–39.9, and 40.0 or above).

Does BMI change with age?

The WHO thresholds themselves stay the same for all adults regardless of age, but body composition shifts as people get older, which is why doctors weigh BMI alongside other factors rather than on its own for older adults.

BMI Calculator

Calculate your BMI (Body Mass Index) instantly. Free online BMI calculator for adults, men and women. Supports metric (kg/cm) and imperial (lb/in) units.

Updated May 2026

BIOSTATS PARAMETERS

Data Entry

Gender

Weight

Height

Age (optional)

yrs

Processing Result

Values calculated using the WHO protocol.

Enter your data on the left to see your technical body mass analysis.

REFERENCE TABLE

< 18.5 Underweight

18.5 – 24.9 Normal Weight

25.0 – 29.9 Overweight

30.0 – 34.9 Obesity Class I

BMI is a screening tool, not a diagnostic measure. Consult a healthcare professional.

Shift + Enter Copy Result

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How to Calculate Your BMI

Metric or imperial units, instant result

1. Pick a unit system

Metric (kg and cm) or Imperial (lbs and feet/inches) — switch anytime.

2. Enter your weight and height

Gender and age are optional and don't change the BMI formula, just the context.

3. Read your result

Your BMI, WHO category, and ideal weight range appear immediately as you type.

What This BMI Calculator Does

Full WHO classification, not just a single number

Metric and imperial support

Enter kg/cm or lbs/ft-in — the calculator converts internally, no manual math needed.

All six WHO BMI categories

Underweight, normal weight, overweight, and three classes of obesity, matched exactly to WHO thresholds.

Ideal weight range, not just a category

Shows the healthy weight interval (BMI 18.5–24.9) for your exact height, so you have a concrete target.

Instant results, no signup

Calculation runs as you type — no submit button required, no account, no email.

Runs entirely in your browser

Weight, height, and age never leave your device — nothing is sent to a server or stored.

BMI Categories (WHO)

The exact thresholds used in the calculation

When You'd Use This

The most common reasons people reach for a BMI calculator

Getting ready for a doctor's appointment

Calculate ahead of time so you walk in already knowing your number and can ask sharper questions.

Tracking a fitness baseline

Use BMI as one simple, repeatable number to watch over weeks or months alongside other measurements.

Insurance or health screening forms

Some policies and workplace wellness checks ask for BMI directly — get the exact figure in seconds.

Planning a nutrition or training goal

Pair your BMI and ideal weight range with a calorie or macro calculator to set a realistic target.

Common Mistake? Start Here

Treating BMI as a diagnosis for athletes

BMI ignores body composition — a bodybuilder can score "overweight" or "obese" while carrying very little body fat.

Using adult BMI thresholds for children

Children and teens need age- and sex-specific percentile charts, not the fixed adult cutoffs used here.

Assuming BMI stays meaningful the same way with age

Muscle mass tends to drop and fat tends to rise with age even at a stable weight — BMI alone won't show that shift.

Why Use This Calculator

It follows the six official WHO BMI categories exactly, with native support for both metric and imperial units — no manual conversion between kg/cm and lbs/ft-in.

It shows the ideal weight range for your specific height, not just which category you fall into, so you get a concrete number to work toward instead of a single isolated score.

Frequently Asked Questions

The WHO healthy range is 18.5 to 24.9 for adults, and it's the same threshold for men and women. The main difference is that women tend to carry more body fat than men at the same BMI, which is one reason BMI alone isn't a full picture.

Resources

WHO — Body Mass Index

Official WHO guidance on healthy weight and BMI classification.

CDC — About Adult BMI

CDC explanation of how BMI is calculated and interpreted for adults.

American Heart Association — BMI in Adults

Clinical context on BMI, its limitations, and how it fits alongside other health measurements.