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About this tool
BMI Prime is your BMI divided by the upper healthy limit, so 1.00 is the ceiling and 1.15 means 15 percent over it.
BMI Prime is body mass index divided by the upper limit of the healthy BMI range, so the answer reads as a plain ratio: 1.00 sits exactly on the ceiling, 1.15 is fifteen percent above it, and 0.90 is ten percent below. This calculator computes BMI as weight in kilograms over height in metres squared, then divides by 25 for the WHO international range or by 23 for the WHO Asia-Pacific range. Because the result is dimensionless it compares cleanly across people of different heights and across the two reference standards.
Open BMI Prime Calculator on AltFTool — it loads instantly in your browser.
Enter the values you already know.
Fine-tune the options to match your scenario.
Read the result and use it in your planning or reporting.
A ratio around 1.00 replaces six categories you would otherwise have to memorise.
Shows BMI Prime against the 25 ceiling and the Asia-Pacific 23 ceiling side by side.
Converts BMI Prime 1.00 into the actual weight for your height, so the gap is actionable.
BMI Prime is your BMI divided by 25, the top of the WHO healthy BMI range. A BMI of 27.5 gives a BMI Prime of 1.10, meaning you are 10 percent above the healthy ceiling. Values below 0.74 correspond to a BMI under 18.5 and are classified as underweight.
Between 0.74 and 1.00 on the WHO scale, which is the same as a BMI of 18.5 to 24.9. Above 1.00 is overweight, 1.20 and above is obesity class I, 1.40 obesity class II and 1.60 obesity class III.
It is the same measurement expressed as a ratio rather than an absolute number. BMI 32 tells you little unless you remember that obesity starts at 30, whereas BMI Prime 1.28 immediately says 28 percent over the limit. Nothing else changes, so it shares BMI's blind spot for muscle mass.
Yes, dividing by 23 rather than 25 is the closer fit. The WHO Asia-Pacific guideline puts the healthy ceiling at 22.9 for South and East Asian populations because diabetes and cardiovascular risk rise at a lower BMI. This calculator offers both references and reports each result.
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