BMI Calculator
Calculate adult body mass index, BMI Prime, the weight range associated with BMI 18.5–24.9 and the weight corresponding to an editable target BMI. BMI is a screening measure, not a diagnosis or direct measurement of body fat.
Adult BMI category table
| BMI | Screening category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to below 25 | Healthy weight |
| 25 to below 30 | Overweight |
| 30 to below 35 | Obesity, class 1 |
| 35 to below 40 | Obesity, class 2 |
| 40 or higher | Obesity, class 3 |
BMI formulas
For metric inputs, BMI = weight (kg) ÷ height² (m²).
For US customary inputs, BMI = 703 × weight (lb) ÷ height² (in²). Internally, the calculator also converts values with 1 lb = 0.45359237 kg and 1 in = 0.0254 m for range and target-weight displays.
BMI Prime is BMI ÷ 25. Weight at a selected BMI is target BMI × height². The displayed BMI 18.5–24.9 range is calculated from height only.
Six checked examples
| Inputs | Checked result |
|---|---|
| 70 kg and 1.75 m | BMI = 22.86; healthy-weight screening category |
| 200 lb and 5 ft 10 in | BMI = 28.70 using the 703 formula |
| 60 kg and 1.65 m | BMI = 22.04 |
| 100 kg and 1.80 m | BMI = 30.86; obesity class 1 screening category |
| Height 1.75 m, BMI range 18.5–24.9 | Associated weight range = 56.66–76.26 kg |
| Height 1.75 m, target BMI 23 | Corresponding weight = 70.44 kg |
Important limits
- BMI is a screening value. It does not directly measure body fat, fitness, fat distribution or health.
- The same adult formula is used for women and men. There is no separate mathematical “female BMI” formula.
- Muscular people, older adults, pregnant people and people with unusual body composition may need other assessments.
- Children and teens require age- and sex-specific percentile evaluation; this adult calculator intentionally rejects ages below 20.
- Risk can vary at the same BMI by individual and population. A clinician can interpret BMI alongside waist measurement, history, laboratory results and other factors.
Sources
Related tools: Calorie Calculator, Pace Calculator and Percentage Calculator.
Questions
Is there a different BMI formula for women?
No. The adult weight-to-height formula and standard screening categories are the same. Health interpretation can still depend on individual context.
What does BMI Prime mean?
It divides BMI by 25. A BMI Prime of 1.00 corresponds to BMI 25; it is another way to express the same height-weight relationship.
Does the displayed weight range guarantee health?
No. It only reverses BMI 18.5–24.9 for the entered height. It is not a personalized target or diagnosis.
Why is age required if it is not in the formula?
Age confirms that the adult categories apply. People below 20 need a percentile-based method.
Body composition estimate
BMI does not directly measure fat mass. Use the Body Fat Calculator for a separate adult circumference estimate, BMI-based comparison, estimated fat mass and lean mass.