BMI Calculator
Calculate your Body Mass Index from height and weight.
This tool runs entirely in your browser. Your files are never uploaded to a server.
BMI is a simple screening ratio, not a diagnosis — it does not account for muscle mass, bone density, age, sex or body composition, and these adult categories don't apply to children or teens. This is not medical advice.
24.2
Normal weight
What this calculator does
Computes Body Mass Index from height and weight in metric or imperial units, and reports the standard adult weight category associated with that BMI value.
How to use it
Choose metric (cm/kg) or imperial (ft/in, lb) units, then enter height and weight. Switching units swaps to that system's fields; the calculation always converts to meters and kilograms internally before applying the formula.
Worked example
A height of 170 cm and weight of 70 kg gives a BMI of about 24.2, in the normal weight range. The imperial equivalent, 5 ft 7 in and 154 lb, gives about 24.1 — the tiny difference comes from rounding in those approximate imperial inputs. Automated tests verify both figures.
Formula
BMI = weight (kg) ÷ height (m)². Imperial height and weight are converted to meters (1 inch = 0.0254 m) and kilograms (1 pound = 0.453592 kg) before the same formula is applied, so results are consistent across both unit systems.
Category thresholds
Under 18.5 is classified underweight, 18.5 to 24.9 is normal weight, 25 to 29.9 is overweight, and 30 or above is obese. These thresholds come from the World Health Organization's international BMI classification for adults and are also used by the U.S. Centers for Disease Control and Prevention.
Limitations
BMI is a population-level screening ratio, not a diagnosis. It does not distinguish muscle from fat, so it can misclassify muscular athletes as overweight, and it does not account for bone density, body-fat distribution, sex or age. These adult thresholds do not apply to children or teens, who are assessed with age- and sex-specific percentile growth charts instead.
Scope, sources and privacy
This is an educational estimate, not a medical diagnosis or professional health advice. The formula and category thresholds were checked against World Health Organization and CDC adult BMI guidance. Reviewed September 2026. Calculation runs locally in your browser; Quiklio does not upload the entered values. Talk to a qualified healthcare professional about what a healthy weight range means for you specifically.
Frequently Asked Questions
- How is BMI calculated?
- BMI = weight (kg) / height (m)². For imperial units, height and weight are converted to metric first.
- Is BMI accurate for everyone?
- BMI is a general screening tool and doesn't account for muscle mass, bone density, age or sex — it may misclassify athletes or older adults.
- What are the BMI categories?
- Under 18.5 is underweight, 18.5-24.9 is normal, 25-29.9 is overweight, and 30+ is obese.