BMI Calculator
Use this BMI calculator to find your body mass index from your weight and height, in pounds and feet/inches or in kilograms and centimeters. You get your BMI, the adult weight category used by the CDC and the World Health Organization, the healthy weight range for your height and your BMI Prime. It is a quick screening number for adults, not a diagnosis.
Updated
Results
- Healthy weight (min)BMI 18.5 at your height
- Healthy weight (max)BMI 24.9 at your height
- BMI PrimeBMI ÷ 25
Results are estimates. See the methodology below.
How to use the BMI calculator
- Choose Imperial (lb, ft/in) or Metric (kg, cm). Imperial is selected by default.
- Enter your weight, ideally measured in the morning in light clothing.
- Enter your height without shoes: feet in the first box, inches in the second. If you are exactly 5 or 6 feet tall, leave inches at 0.
- Read your results: BMI to one decimal, your weight category, the weight range that matches a BMI of 18.5 to 24.9 at your height, and your BMI Prime.
How BMI is calculated
BMI is your weight divided by the square of your height:
- Metric: BMI = weight (kg) ÷ height (m)²
- Imperial: BMI = 703 × weight (lb) ÷ height (in)²
The factor 703 converts lb/in² into kg/m². The calculator uses the exact conversions (1 lb = 0.45359237 kg, 1 in = 2.54 cm), so its unrounded result can differ from the 703 shortcut by a few thousandths.
BMI is rounded to one decimal before it is classified, which is how it is normally reported. That matters at the edges: a raw value of 24.96 is shown as 25.0 and falls in the overweight range.
Adult BMI categories (CDC and WHO)
| Category | BMI |
|---|---|
| Underweight | Below 18.5 |
| Healthy weight | 18.5–24.9 |
| Overweight | 25.0–29.9 |
| Obesity, class 1 | 30.0–34.9 |
| Obesity, class 2 | 35.0–39.9 |
| Obesity, class 3 | 40.0 or higher |
The healthy weight range is the span of weights that would give you a BMI from 18.5 to 24.9 at your current height. BMI Prime is your BMI divided by 25, the upper limit of the healthy range: 1.00 means you are right at that limit, 0.90 means 10% below it and 1.20 means 20% above it.
BMI examples
5 ft 9 in, 160 lb
BMI is 23.6, in the healthy weight range. At this height, a healthy weight runs from 125.3 to 168.6 lb, and BMI Prime is 0.95.
5 ft 4 in, 175 lb
BMI is 30.0 (30.04 before rounding), which is obesity class 1. The healthy range at 5 ft 4 in is 107.8 to 145.1 lb, and BMI Prime is 1.20. At 174 lb the BMI would be 29.9, classified as overweight: one pound changes the label, not your health.
Metric: 175 cm, 70 kg
BMI is 22.9, healthy weight. The healthy range is 56.7 to 76.3 kg, and BMI Prime is 0.91.
What BMI can and can't tell you
BMI is a screening tool. According to the CDC, it does not measure body fat directly and cannot tell fat from muscle or bone, or show where fat is stored. Keep these limits in mind:
- Children and teens: for ages 2 through 19, BMI is interpreted with sex- and age-specific percentiles. This calculator does not compute percentiles, so its adult categories do not apply to anyone under 20.
- Athletes and muscular builds: muscle is dense, so a lean, muscular person can land in the overweight range without excess fat.
- Older adults: people tend to lose muscle and some height with age, so BMI may underestimate body fat, and the BMI linked to the lowest risk may be somewhat higher than in younger adults.
- Pregnancy: BMI is not meaningful during pregnancy. Clinicians use your pre-pregnancy BMI to guide recommended weight gain.
- Ethnicity: a 2004 WHO expert consultation found that many Asian populations face a higher risk of type 2 diabetes and heart disease at BMIs below 25. It kept the international cut-offs but proposed extra public health action points at 23, 27.5, 32.5 and 37.5.
Waist size, blood pressure, blood sugar and family history give a fuller picture. If your result worries you, talk to your doctor.
Frequently asked questions
What is a healthy BMI for adults?
For adults 20 and older, the CDC and WHO consider a BMI from 18.5 to 24.9 a healthy weight. Below 18.5 is underweight, 25.0 to 29.9 is overweight and 30.0 or higher is obesity.
How do I calculate BMI with pounds and inches?
Multiply your weight in pounds by 703, then divide by your height in inches squared. For someone 5 ft 9 in (69 inches) and 160 lb: 703 × 160 = 112,480, and 69² = 4,761, so BMI = 112,480 ÷ 4,761 ≈ 23.6.
Is BMI the same for men and women?
Yes. Adults use the same formula and categories regardless of sex, although at the same BMI women tend to carry more body fat than men.
Can I use this BMI calculator for my child or teenager?
No. For ages 2 through 19, BMI has to be compared with growth-chart percentiles for the child's age and sex. Use the CDC Child and Teen BMI Calculator or ask your pediatrician.
Is BMI accurate if I lift weights?
Often not. BMI only knows weight and height, so extra muscle can push you into the overweight range. Waist circumference or a body composition test shows more.
What does BMI Prime mean?
BMI Prime is your BMI divided by 25. It shows how far you are from the top of the healthy range: under 1.00 is below that limit, over 1.00 is above it. A BMI Prime of 1.20 means your BMI is 20% above 25.
Sources
This calculator is for general information only and is not medical advice. Talk to a doctor or other qualified health professional about your weight and health.