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What is BMI Calculator?

Free BMI calculator. Enter weight and height in metric or imperial to get your BMI, WHO category, BMI Prime, and healthy weight range for your height. No signup.

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BMI Calculator runs entirely in your browser using JavaScript (browser). Your data never leaves your device.

Free BMI Calculator

Calculate your Body Mass Index instantly in metric (kg/cm) or imperial (lb/ft+in) with one-click unit toggle. See your WHO category, BMI Prime (your ratio to the upper-normal boundary of 25), your healthy weight range for your exact height, and a visual category bar showing where you fall. Both metric and imperial supported — no conversion needed.

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Your BMI

22.9

Normal (18.5–24.9)

BMI scale (0–50)

018.525304050+

BMI Prime

0.91

ratio to upper-normal (25)

Healthy weight range

56.7–76.3 kg

BMI 18.5–24.9 for your height

Want to go deeper?

Check your Fitness Age or explore more free fitness calculators on RowGress.

All calculations run in your browser. No data is sent to any server.

Frequently Asked Questions

The World Health Organization defines a healthy BMI as 18.5 to 24.9. Below 18.5 is considered underweight, 25–29.9 is overweight, and 30 or above is obese. These ranges apply to most adults aged 18–65.
BMI is a useful population-level screening tool but has well-known limitations. It cannot distinguish fat mass from lean mass, so muscular athletes often register as "overweight" despite having very low body fat. It also does not account for fat distribution — abdominal (visceral) fat carries higher health risk than fat elsewhere. Use BMI as one data point alongside waist circumference, body fat percentage, and a conversation with your doctor.
The standard WHO BMI scale uses the same ranges for both men and women. However, at the same BMI, women typically carry more body fat than men. Some clinicians use sex-specific body fat thresholds alongside BMI, which is why tools like the body fat calculator provide additional context.
BMI is less accurate for athletes with high muscle mass. A competitive powerlifter or bodybuilder may have a BMI in the "overweight" or "obese" range while having very low body fat. For athletes, direct body composition measures (DEXA scan, hydrostatic weighing, or Navy body fat method) are more meaningful than BMI alone.
BMI Prime is your BMI divided by 25 (the upper limit of the normal range). A BMI Prime of 1.0 means you are exactly at the normal/overweight boundary. Values below 1.0 are in the normal range; values above 1.0 are overweight or obese. It is a simple way to express how far above or below the normal limit you are as a single ratio.
The healthy weight range is calculated by finding the weights that correspond to a BMI of exactly 18.5 and 24.9 for your height. For example, at 5'10" (178 cm), the healthy range is approximately 129–174 lb (58.5–78.9 kg). This gives you a concrete weight target rather than just a category label.

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Understanding Your BMI

Body Mass Index (BMI) is a simple ratio of weight to height squared. It was developed by Adolphe Quetelet in the 1830s as a population-level measure, not a clinical diagnostic tool. The WHO adopted it as a screening metric because it correlates reasonably well with body fat at a population level and requires nothing more than a scale and a tape measure.

WHO BMI Categories

  • Under 18.5 — Underweight. May indicate insufficient caloric intake, underlying illness, or malabsorption. Consult a doctor if you fall in this range.
  • 18.5–24.9 — Normal weight. Associated with the lowest risk for weight-related health conditions in most adults.
  • 25.0–29.9 — Overweight. Elevated risk for type 2 diabetes, cardiovascular disease, and hypertension, particularly with central (abdominal) fat distribution.
  • 30.0–34.9 — Obese Class I. Moderately elevated health risk.
  • 35.0–39.9 — Obese Class II. Severely elevated risk.
  • 40+ — Obese Class III. Very severely elevated risk, often associated with significant comorbidities.

Limitations of BMI

BMI does not measure body fat directly. A 200 lb competitive powerlifter and a 200 lb sedentary adult of the same height will have identical BMIs, despite vastly different body compositions. For a more complete picture, pair BMI with a body fat percentage estimate and waist circumference measurement. Central obesity (high waist-to-hip ratio) is often a stronger predictor of cardiometabolic risk than BMI alone.

What Is BMI Prime?

BMI Prime is your BMI divided by 25. A value of exactly 1.0 means you sit at the boundary between normal and overweight. Values below 1.0 are in the normal range; above 1.0 means overweight or obese. It is a convenient single number that expresses not just your category but how far into — or out of — the healthy range you are.

Go Beyond BMI

BMI is a starting point. For a fuller picture of your fitness, check your Fitness Age on RowGress — it factors in cardiovascular capacity and training history alongside body composition. You can also explore all free fitness calculators on RowGress including body fat, VO2 max, and more.