At 40kg the BMI depends entirely on height, and across the plausible adult range it runs from 17.8 at 150cm down to 10.0 at two metres. Which means something worth saying plainly: 40kg sits inside the healthy BMI band only for heights between 127 and 147cm. That upper bound is shorter than almost any adult, so for pra..
= 5ft 8.9in
YOUR RESULTS
BODY MASS INDEX
13.1
Severely Underweight
BMI PRIME
0.52
Normal = 0.74–1.00
PONDERAL INDEX
7.5
kg/m³
HEALTHY WEIGHT RANGE
56.7 – 76.3 kg
Gain 16.7 kg to reach healthy weight
Significantly below a healthy weight. Medical attention recommended.
BMI GAUGE
YOUR POSITION
FULL SUMMARY
WHO BMI CATEGORIES
The weight is already set to 40kg, which is about 88 pounds. Enter your height and the BMI follows — until you do, the figure is undetermined.
Both unit systems are seeded, so switching between kilograms and pounds keeps the same weight rather than reverting to a default.
Read the band of heights rather than any single BMI. At 40kg the healthy band runs 127 to 147cm, and that band is what a weight actually determines.
A reading near a category boundary should be read as near a boundary. Most people vary by one to two kilograms across a day from food and fluid alone.
At 40kg — about 88 pounds — the BMI is undetermined until a height is supplied. At 150cm it is 17.8, at 175cm 13.1, and at 200cm 10.0: a spread of 7.8 points from one unchanged weight, which is wider than the entire healthy band. Inverting the formula gives what a weight can determine: 40kg sits inside the healthy BMI band for heights between 127cm and 147cm, a window 20cm wide, or roughly 4ft 2in to 4ft 10in. On the WHO 2004 cut-offs for South and East Asian populations the shortest suitable height rises to 132cm, because those thresholds lower the top of the BMI band while leaving 18.5 in place.
FORMULA REFERENCE TABLE
| Name | Formula | Description |
|---|---|---|
| BMI (Metric) | BMI = weight(kg) / height(m)² | Divide weight in kg by height in metres squared |
| BMI (Imperial) | BMI = 703 × weight(lbs) / height(in)² | Multiply weight in pounds by 703, divide by height in inches squared |
| Height in metres | h(m) = h(cm) / 100 | Convert centimetres to metres before squaring |
| BMI Prime | BMI Prime = BMI / 25 | Ratio of BMI to upper limit of normal (25). Values >1.00 indicate overweight |
| Ponderal Index | PI = weight(kg) / height(m)³ | More accurate than BMI for very tall or short individuals. Normal: 11–15 kg/m³ |
| Healthy weight | w = BMI × height(m)² | Rearranged BMI formula: weight(kg) for any target BMI at your height |
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Last updated: August 2, 2026 · Formula verified by EagleCalculator team · Source: WHO Global Database on Body Mass Index · Eagle-eyed accuracy for every calculation.