How to use
- 1Choose Imperial (ft, in, lb) or Metric (cm, kg).
- 2Enter your height and weight.
- 3Read your BMI, its WHO category and your BMI Prime.
- 4See the healthy weight range for your height and how far you are from it.
How BMI is calculated
Body mass index is weight in kilograms divided by the square of height in metres (kg ÷ m²). In US units the equivalent formula is 703 × weight in pounds ÷ height in inches squared. For example, someone 5 ft 10 in (70 in) tall who weighs 170 lb has a BMI of 703 × 170 ÷ 4,900 ≈ 24.4. BMI Prime divides your BMI by 25, the upper limit of the normal range: 1.00 marks that boundary, and roughly 0.74 to 0.99 is the normal band.
WHO categories for adults
The World Health Organization classifies adult BMI as follows: below 18.5 underweight; 18.5–24.9 normal weight; 25–29.9 overweight (pre-obese); 30–34.9 obesity class I; 35–39.9 obesity class II; 40 and above obesity class III. The CDC uses the same cut-offs for adults. The healthy weight range shown for your height is the span of weights that would give a BMI from 18.5 to 24.9 — for 5 ft 10 in, about 129 to 174 lb.
What BMI does not tell you
BMI is a quick screening number, not a diagnosis. It doesn’t distinguish muscle from fat, so muscular athletes can be classed as overweight, while older adults who have lost muscle can fall in the normal range despite a high body-fat percentage. It also says nothing about where fat is stored; waist circumference and body-fat measurements add useful context. For children and teens, BMI has to be read against age- and sex-specific percentiles (CDC growth charts or the WHO growth reference), which this calculator does not support. This tool is for information only and is not medical advice — talk to a doctor or registered dietitian about your weight and health.
Frequently asked questions
What is a healthy BMI?
For adults, the WHO normal range is 18.5 to 24.9. The calculator shows the weight range that corresponds to it for your height.
How do I calculate BMI in pounds and inches?
Multiply your weight in pounds by 703, then divide by your height in inches squared — or switch the calculator to Imperial and enter feet, inches and pounds.
Is BMI accurate for athletes?
Not very. BMI counts all weight the same, so people with a lot of muscle can have a high BMI without excess body fat.
Can I use this BMI calculator for children?
No. Under 18, BMI is judged against age- and sex-specific percentiles. Use the CDC BMI-for-age charts or the WHO growth reference linked in the tool, and ask your pediatrician.
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