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BMI Calculator

Calculate your Body Mass Index (BMI) from your height and weight, see your weight category, and find your healthy weight range — in US or metric units.

years

Adults 20 and older. This calculator uses adult WHO categories, not CDC child percentiles.

Gender

Does not change adult BMI; used for context.

ft
in
lb

BMI

Normal

23.0kg/m²

Healthy BMI range
18.5 – 25 kg/m²
Healthy weight for your height
128.9 – 174.2 lb
BMI Prime
0.92
Ponderal Index
12.9kg/m³
BMI23.0 kg/m²View results

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.

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, which holds up better for very tall or very short people.

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.

BMI categories for adults

BMI (kg/m²)Category
Below 16Severe Thinness
16 – 17Moderate Thinness
17 – 18.5Mild Thinness
18.5 – 25Normal
25 – 30Overweight
30 – 35Obese Class I
35 – 40Obese Class II
40 and aboveObese Class III

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.

Frequently asked questions

What is BMI?
Body Mass Index (BMI) is a number derived from your weight and height (kg ÷ m²). It's a quick, inexpensive screening tool that sorts adults into weight categories — underweight, normal, overweight, and obese — that correlate with health risk at the population level.
What is a healthy BMI?
For most adults a BMI from 18.5 to 25 kg/m² is considered the healthy range. Below 18.5 is underweight and 25 or above is overweight, with 30+ classed as obese.
Is BMI accurate?
BMI is a useful screen, not a diagnosis. Because it only uses height and weight it can't tell muscle from fat — very muscular people may read as "overweight" while others with low muscle may read "normal" despite excess fat. Age, sex, and ethnicity also affect what's healthy.
Does BMI differ by age and sex?
The adult BMI formula and categories are the same for men and women aged 20+. This calculator reports those adult WHO categories. It does not apply CDC growth-chart percentiles used for children ages 2–19.
What are BMI Prime and the Ponderal Index?
BMI Prime is your BMI divided by 25 (the upper healthy limit), so 1.0 is the boundary and below 1.0 is within range. The Ponderal Index uses height cubed instead of squared, which makes it more reliable at the extremes of height.

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