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The formula
New BMI = 1.3 × weight (kg) ÷ height (m)^2.5
The 1.3 is chosen so that, for someone of average height (about 1.69 m), the new BMI matches the classic one.1
Why change the power?
Trefethen argued that people don't scale up evenly in all directions: weight grows faster than height squared but slower than height cubed. With a power of 2, short people's BMIs read a little low and tall people's a little high, so tall people may be told they're heavier than they are.1 A power of 2.5 sits in between.
Classic vs. new BMI
For people at a classic BMI of exactly 25:
| Height | Weight | Classic BMI | New BMI |
|---|---|---|---|
| 150 cm | 56.3 kg | 25.0 | 26.5 |
| 165 cm | 68.1 kg | 25.0 | 25.3 |
| 180 cm | 81.0 kg | 25.0 | 24.2 |
| 195 cm | 95.1 kg | 25.0 | 23.3 |
The difference only matters much at the ends of the height range.
| What the new BMI shows | What it doesn't show |
|---|---|
| Weight for height, adjusted for very short and very tall people | How much of your weight is fat and how much is muscle |
| Numbers close to classic BMI for average heights | Where fat is stored, such as around the stomach |
| Whether your classic BMI may read a little high or low for your height | An official category: none exist for it |
Frequently asked questions
Should I use the new BMI instead?
It's interesting to compare, but doctors and guidelines use the classic BMI. If you're very tall or very short, seeing both can help you understand your number.
Does the new BMI change the categories?
No official categories exist for it. Comparing it with the classic cutoffs is approximate. The classic BMI formula.
Sources
This page is for education and is not medical advice. Talk with a healthcare professional about your weight and health.
