BMI Calculator
Calculate your Body Mass Index (BMI) from height and weight, and see which general weight category it falls into.
BMI is a general screening measure and doesn't account for muscle mass, age, or body composition. It is not a diagnosis. See our Disclaimer.
The formula
Metric: BMI = weight (kg) ÷ height (m)². Imperial: BMI = 703 × weight (lb) ÷ height (in)².
Standard BMI categories
- Below 18.5 — Underweight
- 18.5–24.9 — Normal weight
- 25–29.9 — Overweight
- 30 and above — Obesity
Worked example
A person weighing 70 kg at 175 cm (1.75 m) tall has a BMI of 70 ÷ 1.75² ≈ 22.9, which falls in the normal weight range.
Method and sources
The categories are the World Health Organization's standard adult BMI classification (18.5, 25 and 30). The category is read straight from the number, with no adjustment for age, sex, ethnicity or body composition, and some guidelines use different cut-offs for specific populations — ask a healthcare professional how to interpret your result. The worked example was recalculated independently in September 2026.
Limitations of BMI
BMI doesn't distinguish between muscle and fat, so athletes with high muscle mass can show a misleadingly high BMI. It also doesn't account for age, sex, or where fat is distributed on the body. It's best used as a general screening starting point, not a full health assessment.
Entering your numbers
- Metric takes weight in kilograms and height in centimeters. Imperial takes weight in pounds and height in inches only, so 5 ft 7 in is entered as 67 and 5 ft 9 in as 69.
- Both values must be greater than zero. A zero or negative number shows "Please enter positive values."
- BMI is rounded to one decimal place, and the category is a single label: Underweight, Normal weight, Overweight or Obesity.
More worked examples
50 kg at 175 cm gives a BMI of 16.3 (Underweight), and 95 kg at 175 cm gives 31.0 (Obesity). In imperial units, 154 lb at 67 in gives 24.1 and 200 lb at 70 in gives 28.7 (Overweight).
The category is chosen from the unrounded BMI, which can look surprising at a boundary. 76.45 kg at 175 cm is 24.96 before rounding, so it is shown as 25.0 but still labelled Normal weight, because it is below 25. Near the lower cut-off, 56.7 kg at 175 cm shows 18.5 and Normal weight, while 53.6 kg shows 17.5 and Underweight.
What this page does not do
It uses one set of adult cut-offs for everyone and does not ask for age or sex. The Ideal Weight Calculator is a separate tool.
Frequently asked questions
Is BMI accurate for everyone?
No. It's a population-level screening tool that works reasonably well for most adults but can be misleading for athletes, older adults, pregnant women, and children, where other measures are more appropriate.
What should I do if my BMI is outside the normal range?
BMI alone isn't a diagnosis. If you have concerns about your weight or health, a doctor can assess your overall health using additional measures beyond BMI.
Why does my BMI show 25.0 but the category says Normal weight?
The number shown is rounded to one decimal, while the category uses the exact value. A BMI of 24.96 displays as 25.0 yet is still below the 25 cut-off.
How do I enter my height in feet and inches?
Switch to imperial and convert to inches only: multiply the feet by 12 and add the extra inches. 5 ft 9 in becomes 69.