BMI Calculator
The BMI calculator computes your Body Mass Index from your height and weight using the standard formula. Enter your measurements in metric or imperial units, see your result plotted on a visual scale, and read what your BMI category means in practical terms. Free, no account needed.
How to use BMI Calculator
- Select your unit system: metric (kg, cm) or imperial (lbs, ft, in).
- Enter your height and weight in the input fields.
- Your BMI calculates instantly and the gauge updates to your category.
- Read your BMI classification and healthy weight range in the results panel.
- Switch to the WHO reference table to see all BMI categories.
Understanding your BMI result
The body mass index calculator divides your weight in kilograms by the square of your height in metres (kg/m²). The World Health Organization defines the BMI categories as: Underweight, below 18.5, Normal weight, 18.5 to 24.9, Overweight, 25.0 to 29.9, and Obese, 30.0 and above. For adults, these thresholds apply regardless of age or sex. Knowing your category is the starting point for understanding whether your weight is contributing to health risk.
The BMI chart for adults plots your result against the standard category boundaries. A BMI in the normal weight range (18.5–24.9) is associated with the lowest risk of weight-related health conditions in large population studies. A BMI in the overweight range (25–29.9) is associated with moderately increased risk of type 2 diabetes, cardiovascular disease, and hypertension. A BMI of 30 or above is associated with substantially increased risk across multiple chronic conditions.
Limitations of BMI as a health measure
BMI is a screening tool, not a diagnostic measure. It cannot distinguish between fat mass and lean mass. A highly muscular individual with very low body fat may register as overweight or obese on the BMI scale because muscle is denser than fat. Conversely, an individual with a BMI in the normal range can still carry unhealthy levels of visceral fat, a condition known as normal-weight obesity or skinny fat, which carries similar metabolic risks to higher BMI values.
For a more complete picture of body composition, use the BMI result alongside the body fat percentage calculator (which uses the US Navy circumference method) and the ideal weight calculator (which provides healthy weight ranges from four established formulas). The overweight BMI range and healthy BMI range by age data suggest that the thresholds may need adjustment for older adults, for whom a slightly higher BMI may be associated with better outcomes. The calculate my BMI metric result is best interpreted in consultation with a healthcare provider who can account for your individual health history.
Frequently asked questions
The World Health Organization defines a healthy BMI range for adults as 18.5 to 24.9 kg/m². Below 18.5 is classified as underweight. Between 25.0 and 29.9 is classified as overweight. A BMI of 30 or above is classified as obese. These thresholds are the same for all adult men and women and do not change with age, though some research suggests slightly different thresholds may be more appropriate for different ethnic groups and for older adults.
No. BMI is a poor measure of health for highly muscular individuals because it cannot distinguish between fat mass and lean mass. A bodybuilder or professional athlete may have a BMI in the overweight or obese range while carrying very low body fat. For muscular individuals, the body fat percentage calculator using the US Navy circumference method gives a more meaningful measurement of body composition than BMI alone.
The standard WHO BMI categories use the same thresholds for men and women: 18.5–24.9 for normal weight. However, women naturally carry a higher percentage of body fat than men at the same BMI, because BMI does not account for body composition differences between sexes. The body fat percentage calculator accounts for sex in its calculation, which makes it a more sex-specific measure than BMI alone.
A BMI in the overweight range (25–29.9) is worth addressing but does not require drastic action. First, calculate your TDEE to understand your maintenance calorie level, then set a modest calorie deficit using the calorie calculator. Even a 5 to 10 percent reduction in body weight produces meaningful improvements in blood pressure, blood sugar, and cholesterol. Consult a healthcare provider or registered dietitian before making significant changes to your diet or exercise routine.