Calculate your Body Mass Index (BMI) from height and weight. Switch between metric and imperial, see WHO category and healthy weight range - all computed live in your browser.
Technical Specifications
How BMI is calculated and the limits that apply.
| Specification | Details |
|---|
| Metric formula | BMI = weight (kg) / height (m)^2 (height in cm converted to meters (cm / 100) |
| Imperial formula | BMI = 703 x weight (lbs) / height (in)^2 - feet x 12 + inches gives total inches |
| Categories (WHO) | Underweight < 18.5, Normal 18.5-24.9, Overweight 25-29.9, Obese >= 30 (adult 18+) |
| Healthy range | Weight at BMI 18.5 to 24.9 for the entered height; shown in kg and lbs |
| Input range | Height 50-300 cm (1-10 ft) | Weight 10-500 kg (22-1100 lbs) | Decimals accepted, commas ignored |
| Precision | Double-precision; BMI displayed to 1 decimal; range bounds to 1 decimal; marker clamped to 16-40 scale |
| Processing location | 100% client-side JavaScript in your browser memory; nothing is uploaded |
| Usage limit | None - run unlimited calculations for free, no signup required |
Understanding Body Mass Index
Body Mass Index condenses height and weight into a single ratio - weight scaled by height squared - so a 160 cm and a 185 cm person can be compared on the same chart. It is a population screening tool, not a diagnosis, but it correlates with total body fat at group level and predicts risk bands used by WHO and CDC.
Metric vs imperial arithmetic
The definition is kilograms per square meter. When height is in centimeters, divide by 100 to get meters first. In inches and pounds the constant 703 reconciles the units: 703 x lbs / in^2 yields the same index. Our calculator shows both the formula and the substituted numbers, so 70 kg at 175 cm reads as 70 / 1.75^2 = 22.9, and 154 lbs at 5 ft 9 in reads as 703 x 154 / 69^2 = 22.7. For percent-based health budgets see the Percentage Calculator and for timelines the Age Calculator.
Categories and healthy weight range
WHO bands are fixed: below 18.5 is underweight, 18.5-24.9 normal, 25-29.9 overweight, and 30+ obese. The healthy range inverts the formula: low = 18.5 x m^2 and high = 24.9 x m^2. At 175 cm that is 56.7-76.3 kg. The delta stat tells you how many kilograms or pounds to gain or lose to reach the nearest edge of that interval.
Beyond BMI: prime and ponderal
BMI Prime divides BMI by 25, the upper normal limit, so 0.85 is 15% below and 1.2 is 20% above. Ponderal Index uses the cube of height (kg / m^3) and tracks proportionality better in very short or tall builds. Both appear in the stats grid as secondary references.
Honest limitations
Muscle weighs more than fat per volume, so athletes can test as overweight without excess adiposity. Conversely, muscle loss with age can hide fat gain. Pregnancy, edema, amputation and childhood growth require separate charts. Use BMI alongside waist circumference, activity, and clinician guidance rather than as a standalone verdict.
Privacy and Client-Side Security
Privacy Guarantee: All calculations occur locally inside your browser. Your heights and weights are never transmitted, stored, or recorded on remote servers.
Many health calculators send personal measurements to a server for processing, which is unnecessary for a division. TinyToolzz keeps everything in-page: unit conversion, squaring, and classification run with plain JavaScript number operations.
Because nothing is uploaded, there is no waiting, no account, and no copy of your figures retained anywhere. Your values exist only in the tab's memory and are discarded when you close the page or click Clear.