⚖️ BMI Calculator
Enter your weight and height to see your Body Mass Index and which category it falls into — a quick fitness screening check, whether you're training on land or out on the water.
🧮 Calculate Your BMI
What is a BMI Calculator?
Body Mass Index (BMI) is a quick screening measure that relates your weight to your height, giving a general sense of whether you sit in the underweight, normal, overweight, or obese range. Enter your numbers in metric or imperial units and get an instant result.
It's a useful starting point, not a full picture. BMI can't tell muscle from fat, so sailors, rowers, and other athletes with a muscular, low-body-fat frame often read higher than their actual fitness would suggest. Use it as a general guide and pair it with other measures — waist circumference, body-fat percentage, or a trainer's assessment — for a fuller view of your health.
❓ Frequently Asked Questions
How does the BMI calculator work?
Enter your weight and height in either metric (kg, cm) or imperial (lb, in) units. It divides your weight in kilograms by the square of your height in metres to get your Body Mass Index, then places that number into one of four bands: Underweight, Normal, Overweight, or Obese.
What do the BMI categories mean?
For adults, a BMI under 18.5 is classed as Underweight, 18.5 to less than 25 as Normal (CDC calls it Healthy Weight), 25 to less than 30 as Overweight, and 30 or greater as Obese. These are the CDC and World Health Organization adult cut-offs (WHO: overweight is "a BMI greater than or equal to 25" and obesity "a BMI greater than or equal to 30"). The result is shown to two decimals without rounding up, so 24.996 shows as 24.99, inside its own band. BMI is a screening measure, not an individual diagnosis.
Is BMI accurate for muscular athletes or sailors?
Not always. BMI only accounts for total weight relative to height — it can't distinguish muscle from fat. Sailors, rowers, and other athletes with above-average muscle mass and a lean frame often score "Overweight" or higher on BMI despite having low body fat. In those cases, waist circumference, body-fat percentage, or a trainer's assessment give a more accurate picture.
Can I use this BMI calculator for a child or teenager?
No. These categories are for adults. Because children and teens are still growing, CDC classifies BMI for ages 2 through 19 by sex-specific BMI-for-age percentiles, so the same number means different things at different ages. Use CDC's Child and Teen BMI Calculator, and talk to the child's doctor.
Is this medical advice?
No. This tool gives a general fitness estimate for informational purposes only. It doesn't replace a doctor's assessment, and factors like age, sex, bone density, and muscle mass all affect how meaningful a given BMI is for you. Speak to a doctor or qualified trainer for individual guidance.