Free BMI Calculator Online

Calculate your Body Mass Index in metric or imperial units, and instantly see your BMI category, healthy weight range and ideal body weight.

Enter your details to calculate your BMI
Please enter a valid weight and height to calculate your BMI.
Your BMI will appear here
UnderweightNormalOverweightObese
CategoryBMI Range
UnderweightBelow 18.5
Normal weight18.5 – 24.9
Overweight25.0 – 29.9
Obesity Class I30.0 – 34.9
Obesity Class II35.0 – 39.9
Obesity Class III40.0 and above

Understanding Your BMI Result

01BMI is a screening tool, not a diagnosis — it doesn't directly measure body fat percentage, and a single number can't capture the full picture of health.
02Muscle weighs more than fat, so athletes and very muscular people often show a higher BMI despite having low body fat.
03The healthy weight range below is calculated directly from your entered height using the standard 18.5–24.9 normal BMI band.
04Ideal body weight uses the Devine formula, a widely used clinical estimate based on height and gender — treat it as a reference point, not a strict target.
05If your BMI falls outside the normal range, consider discussing it with a healthcare provider who can account for factors this calculator can't, like muscle mass and body composition.

Want to check your age-based health milestones too?

Features

✓Metric (kg/cm) and Imperial (lb/ft-in) support
✓Instant BMI value and WHO category
✓Visual BMI scale with your position marked
✓Healthy weight range for your height
✓Weight to lose or gain to reach normal range
✓Ideal body weight (Devine formula)
✓BMI Prime ratio
✓WHO BMI classification reference table
✓No sign-up, no data stored
✓Fully responsive on any device

A BMI Calculator That Shows More Than Just One Number

Most BMI calculators give you a single figure and leave you to look up what it means. ToolPlex's free BMI calculator works in both metric and imperial units and instantly shows your BMI category, where you fall on the WHO classification scale, your healthy weight range for your exact height, and how much weight you'd need to lose or gain to reach the normal range — all from one entry.

It also estimates your ideal body weight using the Devine formula, a calculation commonly used in clinical settings, giving you a second, gender-specific reference point alongside the standard BMI range.

How BMI Is Calculated

Body Mass Index is calculated by dividing weight in kilograms by height in meters squared. For pounds and inches, the formula multiplies weight by 703 before dividing by height in inches squared — both approaches land on the same standardized BMI scale used worldwide by health organizations.

What Your BMI Category Means

The World Health Organization classifies adult BMI into six bands: underweight below 18.5, normal weight from 18.5 to 24.9, overweight from 25 to 29.9, and three classes of obesity above 30. These ranges are population-level screening categories, useful for spotting broad trends, but they don't account for individual differences in muscle mass, bone density, or body composition.

Why BMI Has Limitations

BMI cannot distinguish between muscle and fat, which is why a muscular athlete and a sedentary person of the same height and weight can receive the identical BMI despite very different body compositions. It also doesn't account for where fat is distributed on the body, which research shows matters for health risk. For these reasons, BMI is best used as a quick screening reference rather than a complete health assessment.

Healthy Weight Range and Ideal Body Weight

The healthy weight range shown by this calculator is simply the weight span that would place your exact height within the normal BMI band. Ideal body weight, by contrast, is a single target figure from the Devine formula, originally developed for clinical drug-dosing calculations and since adopted more broadly as a quick reference weight based on height and gender. Neither figure should be treated as a rigid goal — they're reference points to discuss with a healthcare provider if relevant.

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Frequently Asked Questions