Body Mass Index (BMI) estimates whether your weight is in a healthy range for your height. Enter your height and weight in US or metric units to see your BMI, weight category, healthy weight range, BMI Prime, and Ponderal Index.
Understanding your results
Your BMI is a height-and-weight screening measure. The category describes where that number falls in the adult ranges below; it is not a diagnosis. The healthy weight range reverses the BMI formula for your height and is not a personalized weight target. BMI Prime and Ponderal Index are additional mathematical measures, explained in the formula section.
Read the limitations alongside the result, especially when body composition or age makes adult BMI categories less useful. For a different type of estimate, the Body Fat Calculator uses body measurements rather than BMI alone.
How to calculate and check BMI
Measure height without shoes and weight in light clothing when possible. Select US units for feet, inches, and pounds or metric units for centimetres and kilograms. The two formulas are equivalent apart from unit conversion.
A quick reasonableness check is to square the height in metres, then divide the
weight in kilograms by that value. For 73 kg and 1.78 m, 73 ÷ 1.78² ≈ 23.0.
The result has units of kg/m² even though it is usually referred to simply as a
BMI number.
BMI categories for adults
| BMI (kg/m²) | Category |
|---|---|
| Below 16 | Severe Thinness |
| 16 to less than 17 | Moderate Thinness |
| 17 to less than 18.5 | Mild Thinness |
| 18.5 to less than 25 | Normal |
| 25 to less than 30 | Overweight |
| 30 to less than 35 | Obese Class I |
| 35 to less than 40 | Obese Class II |
| 40 and above | Obese Class III |
The expanded table subdivides values below 18.5. CDC's principal adult screening categories are underweight below 18.5, healthy weight from 18.5 to less than 25, overweight from 25 to less than 30, and obesity at 30 or above, with obesity classes at 30, 35, and 40.
What BMI does not measure
BMI does not directly measure body fat, muscle, bone, fitness, blood pressure, or metabolic health. People with the same BMI can have different body composition and health risks. CDC describes adult BMI as a screening measure that should be considered with other factors rather than used to diagnose disease.
The adult categories apply to people age 20 and older. Children and teens are assessed with age- and sex-specific BMI percentiles, so this adult calculator is not the correct interpretation tool for ages 2–19. Pregnancy, substantial muscle mass, fluid changes, and some medical conditions can also make a standalone BMI less informative.
Use the Body Fat Calculator for a tape-based estimate or the Ideal Weight Calculator to compare several height-based formulas. Each is an estimate with its own limitations.
Examples
5 ft 10 in, 160 lb (US units)
A 5'10" adult weighing 160 lb has a BMI of about 23.0 — squarely in the Normal range. The healthy weight range for that height is roughly 129 – 174 lb.
178 cm, 73 kg (metric)
The same person in metric units (178 cm, 73 kg) also gets BMI 23.0 — the two unit systems agree. The healthy weight range here is about 58.6 – 79.2 kg.
Formula
BMI is your weight divided by the square of your height. Switch units with the tabs above — both forms give the same result:
Metric: BMI = mass(kg) / height(m)²
US: BMI = 703 × mass(lb) / height(in)²
BMI Prime = BMI ÷ 25 (so 1.0 marks the top of the healthy range), and the Ponderal Index = mass(kg) / height(m)³. It is provided as an alternative height-scaled measure, without claiming that it is a better personal health measure.
BMI is a screening tool, not a diagnosis. It can't distinguish muscle from fat, so athletes may read high and it shouldn't replace advice from a clinician.
Healthy-weight range calculation
The displayed range reverses the BMI formula at 18.5 and 25 for the entered height. It is a mathematical screening range, not a personalized target. Clinicians may consider growth history, body composition, medications, health conditions, and other measurements before discussing weight goals.
Sources
The category uses the unrounded BMI. A displayed BMI rounded to 25.0 can still be below 25 internally and remain in the Normal category. Weight-range limits are rounded for display; the upper limit is exclusive.