BMI Calculator
Calculate your Body Mass Index (BMI) from your height and weight in U.S. or metric units.
What is BMI Calculator?
The Body Mass Index (BMI) is a simple screening measurement that relates your weight to your height. It is widely used by U.S. physicians, insurers, and the CDC as a first-pass way to flag underweight, healthy-weight, overweight, and obesity ranges in adults.
BMI is a blunt tool — it does not distinguish muscle from fat, and it can be misleading for athletes and the elderly. Treat it as a starting point, not a diagnosis, and talk to your healthcare provider about what a healthy weight means for you specifically.
Formula
The BMI formula for U.S. units:
BMI = (weight in pounds × 703) ÷ (height in inches)2
For metric units:
BMI = weight in kg ÷ (height in meters)2
CDC category ranges for adults 20 and older:
- Below 18.5 — Underweight
- 18.5 – 24.9 — Normal weight
- 25.0 – 29.9 — Overweight
- 30.0 and above — Obese
Worked example
A person who is 5'9" (69 inches) tall and weighs 170 lb:
- Height squared: 69 × 69 = 4,761
- Weight × 703: 170 × 703 = 119,510
- BMI = 119,510 ÷ 4,761 ≈ 25.1
A BMI of 25.1 falls just inside the Overweight range; a healthy weight at that height is 125–168 lb.
How to use this calculator
- Pick your preferred units — U.S. (feet/inches and pounds) or metric.
- Enter your height.
- Enter your weight. The result updates instantly.
- Compare the BMI value and category to the healthy range shown.
Frequently asked questions
Is BMI accurate for athletes and bodybuilders?
Not always. Muscle is denser than fat, so heavily muscled individuals can register as "overweight" or even "obese" despite having low body fat. For athletes, body-fat percentage, waist-to-height ratio, or DEXA scans are more informative.
What BMI is considered healthy?
The CDC considers a BMI between 18.5 and 24.9 to be a healthy weight for adults. 25.0 to 29.9 is overweight; 30.0 and above is obese (class I 30–34.9, class II 35–39.9, class III 40+).
Does BMI apply to children?
No — children and teens use a different, age- and sex-adjusted BMI-for-age percentile chart published by the CDC. Always consult a pediatrician for children and adolescents under 20.
Does BMI adjust for age or ethnicity?
The standard BMI categories do not. Some research suggests Asian populations face elevated health risks at lower BMI values (overweight at 23+, obese at 27.5+), and older adults may have slightly higher healthy ranges. Use BMI as a screen and discuss specifics with a doctor.
What is a better alternative to BMI?
Waist circumference and waist-to-height ratio are simple alternatives that better reflect abdominal fat, which is more strongly linked to heart disease and diabetes risk. A waist-to-height ratio below 0.5 is generally healthy for adults.