BMI Calculator
Work out your Body Mass Index in seconds. Enter your height and weight below to get your BMI, healthy weight range, BMI Prime, and Ponderal Index — with plain-English guidance underneath.
What is BMI?
Body Mass Index (BMI) is a simple screening measurement that estimates whether your weight is appropriate for your height. It's calculated by dividing your weight by the square of your height, and the result places you into one of several standard categories: underweight, normal weight, overweight, or obese.
BMI doesn't measure body fat directly, and it doesn't account for muscle mass, bone density, or where fat is distributed on the body. Even so, it correlates reasonably well with more direct measures of body fat for most people, which is why doctors, insurers, and public health bodies use it as a fast, low-cost first check. Think of it as a starting point for a conversation about health, not a diagnosis on its own.
BMI table for adults
The table below follows the World Health Organization's classification, used for both men and women aged 20 and over.
| Classification | BMI range (kg/m²) |
|---|---|
| Severe thinness | < 16 |
| Moderate thinness | 16 – 17 |
| Mild thinness | 17 – 18.5 |
| Normal weight | 18.5 – 25 |
| Overweight | 25 – 30 |
| Obese Class I | 30 – 35 |
| Obese Class II | 35 – 40 |
| Obese Class III | > 40 |
BMI for children and teens (age 2–20)
BMI works differently for growing bodies, so children and teenagers aren't measured against the fixed adult table. Instead, the CDC compares a child's BMI to other children of the same age and sex, producing a percentile.
| Category | Percentile range |
|---|---|
| Underweight | < 5th percentile |
| Healthy weight | 5th – 85th percentile |
| At risk of overweight | 85th – 95th percentile |
| Overweight | > 95th percentile |
Because growth rates vary so much between children, a pediatrician is the right person to interpret a child's BMI-for-age result — this calculator is intended for adult use.
Health considerations at either end of the scale
Being overweight
- Higher blood pressure and elevated LDL ("bad") cholesterol
- Increased risk of type II diabetes
- Greater strain on the heart and circulatory system
- Joint stress, which can accelerate osteoarthritis
- Higher likelihood of sleep apnea and breathing difficulty
- Elevated risk for several cancers and gallbladder disease
Being underweight
- Nutrient deficiencies and reduced immune function
- Lower bone density, raising fracture risk over time
- Anemia and reduced ability to carry oxygen in the blood
- Fertility and menstrual cycle disruption
- Slower recovery from illness or surgery
- In children, potential impact on growth and development
If your BMI sits well outside the normal range, or if being under- or overweight doesn't seem to have an obvious explanation, it's worth talking to a doctor rather than trying to self-diagnose the cause.
Limitations of BMI
BMI is useful precisely because it's simple — but that simplicity is also its biggest weakness. It cannot distinguish muscle from fat, so a muscular athlete and a sedentary person of the same height and weight will get an identical score, even though their actual body composition is very different.
- Athletes and bodybuilders often register as "overweight" despite having low body fat, because muscle is denser than fat.
- Older adults tend to carry more body fat than younger adults at the same BMI, since muscle naturally declines with age.
- Sex differences mean women typically carry a higher percentage of body fat than men at an equivalent BMI.
- Fat distribution matters for health risk — BMI can't tell the difference between fat carried around the waist versus the hips.
For these reasons, BMI is best used alongside other measurements — waist circumference, body fat percentage, or a conversation with a healthcare provider — rather than as a stand-alone verdict on someone's health.
BMI formula
BMI is calculated the same way worldwide; only the units change. Below, both formulas are shown using a 5'10", 160 lb (1.78 m, 72.6 kg) individual as an example.
BMI Prime & Ponderal Index
BMI Prime
BMI Prime expresses your BMI as a ratio against the upper limit of "normal" (25 kg/m²). A value under 1.0 means your BMI falls within the normal range; a value of exactly 1.0 sits right at the boundary of overweight.
Ponderal Index
The Ponderal Index (PI) is a close cousin of BMI that cubes height instead of squaring it. That makes it more reliable than BMI at the extreme ends of the height range, since it scales more accurately for very tall or very short individuals.
Frequently asked questions
Is BMI accurate for everyone?
No. BMI is a population-level screening tool. It tends to be less accurate for athletes, older adults, pregnant women, and people with unusually high or low muscle mass. It's a useful starting indicator, not a precise diagnostic measurement.
What is a "healthy" BMI?
For most adults, a BMI between 18.5 and 25 kg/m² is classified as normal weight by the World Health Organization. This calculator shows your exact healthy weight range in kilograms or pounds based on your height.
Does BMI differ by age or gender?
The standard adult BMI thresholds are the same for men and women aged 20+. However, health outcomes at a given BMI can differ by age and sex, which is one reason BMI shouldn't be read in isolation.
How is BMI different from body fat percentage?
BMI is calculated purely from height and weight. Body fat percentage measures the actual proportion of fat in your body, usually via skinfold calipers, bioelectrical impedance, or a DEXA scan, and is a more direct — but less convenient — measurement.
Popular Search Terms & Keywords
People who used this calculator also searched for:
