BMI Calculator
Calculate your Body Mass Index (BMI) from your height and weight and see your WHO weight category instantly. Free, private BMI calculator for adults.
Important Information
Body Mass Index (BMI) is a simple index of weight-for-height that is commonly used to classify underweight, overweight and obesity in adults. It is defined as the weight in kilograms divided by the square of the height in metres ($kg/m^2$).
About this tool
Compute your Body Mass Index from height and weight — metric or imperial — using the WHO-standard formula, with your result placed on the underweight-to-obese scale and explained in plain language. It's a thirty-second screening check, honest about being exactly that.
How to Calculate Your BMI
- 1
Enter your height and weight in whichever system you think in — centimeters and kilograms, or feet, inches, and pounds.
- 2
The index is computed as weight divided by height squared, the formula health organizations worldwide standardize on.
- 3
See your BMI value, which WHO category it falls in, and what that classification does and doesn't mean.
Why Check BMI with Wrklyst
- Health Numbers Kept to Yourself
- Height and weight are computed in your browser and go nowhere — no health-data profile accumulates anywhere.
- Both Unit Systems, Zero Math
- Imperial entries are converted internally, sparing you the feet-to-meters arithmetic that derails hand calculation.
- Context, Not Just a Number
- The category explanation frames what the figure suggests — more useful than a bare 24.7 floating alone.
Sensible BMI Use
- Weigh at the same time of day when tracking — daily fluctuation is a kilogram or more.
- Watch the trend across months rather than reacting to any single reading.
- Pair BMI with a waist measurement; together they screen better than either alone.
- Use it as a prompt for doctor conversations, never as a substitute for one.
Frequently asked questions
What do the BMI categories mean?
WHO's adult ranges: below 18.5 is classed underweight, 18.5–24.9 the healthy reference range, 25–29.9 overweight, and 30+ obese. These are population-level screening bands — statistical associations with health outcomes — rather than individual diagnoses, which is why doctors treat them as a starting point for conversation.
Why does BMI mislabel muscular people?
The formula sees only mass and height — it can't distinguish muscle from fat, and muscle is denser. Athletes routinely register overweight while carrying little fat; conversely, a sedentary person can hold a normal BMI with high fat percentage. Waist measurements and body-composition scans fill in what BMI can't see.
Does BMI apply to children and older adults?
Differently. Children's BMI is interpreted through age-and-sex percentile charts, not adult cutoffs — a pediatrician's tool. For older adults, evidence suggests slightly higher BMIs associate with better outcomes, and muscle loss skews readings. The adult ranges here fit adults of working age best.
My BMI is borderline — should I worry?
A single point near a boundary is noise, not news: BMI's usefulness is in trend and context, not decimal precision. Track it over months, note the direction, and weigh it alongside energy, fitness, waist size, and bloodwork. Any genuine concern belongs in a conversation with a doctor, not a category label.