Enter your height and weight to calculate your BMI Prime — a ratio that compares your BMI directly to the upper limit of the normal range (25). Choose between Imperial (feet, inches, pounds) or Metric (cm, kg) units. You get back your BMI Prime value, your underlying BMI, and your weight category based on WHO classification.
BMI Prime
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BMI
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Weight Category
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Normal Weight Range (lower)
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Normal Weight Range (upper)
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BMI Prime is a dimensionless ratio of your actual BMI to the upper limit of the normal BMI range (25). A BMI Prime of 1.0 means your BMI is exactly 25. Values below 1.0 indicate normal or underweight, while values above 1.0 indicate overweight or obesity. It was designed to make it easier to instantly understand how far you are from the normal range.
BMI Prime is calculated by dividing your BMI by 25 (the upper boundary of the normal BMI range). First, your BMI is computed using the standard formula: weight (kg) divided by height (m) squared. Then that result is divided by 25 to give the BMI Prime ratio.
A BMI Prime between 0.74 and 1.00 is considered the normal (healthy) range, corresponding to a BMI of 18.5 to 25. A value below 0.74 suggests underweight, while a value above 1.00 indicates overweight or obesity according to WHO classifications.
Regular BMI is an absolute number (e.g. 22.5) that requires you to know the normal range to interpret. BMI Prime is a ratio anchored to the normal upper limit of 25, so a value of 1.0 always means you are exactly at the boundary of normal weight. This makes BMI Prime quicker to interpret at a glance.
BMI Prime, like standard BMI, is designed for adults aged 18 and over. It is not suitable for children, pregnant women, or highly muscular individuals, as BMI-based measures do not distinguish between fat mass and muscle mass and can be misleading in these groups.
BMI Prime categories follow WHO classifications: Severe thinness (< 0.64), Moderate thinness (0.64–0.67), Mild thinness (0.68–0.73), Normal range (0.74–1.00), Overweight/Pre-obese (1.00–1.20), Obese Class I (1.20–1.40), Obese Class II (1.40–1.60), and Obese Class III (≥ 1.60).
Yes, exactly. BMI Prime = BMI / 25. The divisor 25 represents the upper boundary of the normal BMI range as defined by the World Health Organization. Because of this simple relationship, BMI Prime is a linear rescaling of BMI and carries the same limitations.
A BMI Prime above 1.00 corresponds to a BMI above 25, which WHO classifies as overweight or obese. However, BMI and BMI Prime do not directly measure body fat percentage. Athletes with high muscle mass may have elevated BMI Prime values without excess body fat, so it should be interpreted alongside other health assessments.