A free BMI calculator that runs entirely in your browser. Enter your height and weight in metric (cm/kg) or imperial (ft/in, lb) units to instantly see your Body Mass Index, which category it falls into (underweight, normal, overweight, or obese), where you sit on the BMI scale, and the healthy weight range for your height. Nothing is uploaded — all the math happens on your device.
BMI is a general screening tool, not a diagnosis. It doesn’t distinguish muscle from fat, so athletes, older adults, and pregnant women may be misclassified — talk to a healthcare professional about what your number means for you.
How to use this BMI calculator
Pick your unit system — Metric (height in centimetres, weight in kilograms) or Imperial (height in feet and inches, weight in pounds) — then enter your height and weight. The tool instantly shows your BMI, the category it falls into, a marker on the BMI scale, and the healthy weight range for your height. Switching units converts your entries automatically, and everything is calculated in your browser — nothing is sent to a server.
What your BMI means: the categories
Body Mass Index (BMI) is your weight in kilograms divided by the square of your height in metres (kg/m²). The World Health Organization groups adult BMI into four standard categories:
- Underweight: BMI below 18.5
- Normal weight: BMI 18.5 – 24.9
- Overweight: BMI 25 – 29.9
- Obese: BMI 30 or above
BMI is a quick population-level screening measure, not a body-composition test. It can't tell muscle from fat, so a muscular athlete can read as "overweight" while carrying very little fat, and it isn't designed for children, pregnant women, or very elderly people. Treat your number as a starting point for a conversation with a healthcare professional, not a verdict.
Frequently asked questions
How is BMI calculated?
BMI = weight (kg) ÷ height² (m²). For example, 70 kg at 1.75 m gives 70 ÷ (1.75 × 1.75) ≈ 22.9. If you use imperial units, this tool converts feet/inches and pounds to metres and kilograms first, then applies the same formula — equivalent to the common shortcut BMI = 703 × lb ÷ in².
Is BMI accurate? What are its limitations?
BMI is a useful screening tool at the population level, but it has real limitations for individuals: it doesn't distinguish muscle from fat, doesn't account for where fat is stored, and the standard cut-offs don't fit everyone equally (age, sex, and ethnicity all shift what a "healthy" number looks like). A high or low BMI is a reason to look closer — with waist measurements, body-fat estimates, or a doctor's assessment — not a diagnosis by itself.
What is a healthy BMI range?
For most adults, a BMI between 18.5 and 24.9 is considered the healthy range. This calculator also translates that range back into actual weight for your height — for example, at 175 cm the healthy range is roughly 56.7–76.3 kg (about 125–168 lb).
Is this BMI calculator free and private?
Yes — it's completely free, with no signup. All calculations run locally in your browser using plain JavaScript; your height and weight are never uploaded or stored on any server.
More free tools
Browse the full set of free GeoParrot tools, or try the percentage calculator for quick percent math like weight-change percentages.