How to Read a BMI Chart (And Why It's Often Wrong)

A BMI chart looks simple: find your height, find your weight, read the colour. What the colours do not tell you is why the same square means different things for different people.

How the grid is built

Rows are height, columns are weight, and each cell holds weight ÷ height². Colour bands mark the standard adult categories: under 18.5, 18.5–24.9, 25–29.9 and 30+.

Reading it correctly in 3 steps

1) Use height without shoes, measured in the morning. 2) Use weight in light clothing on the same scale each time. 3) Read the cell, then read the whole row — see how many kilos separate you from the next band.

Why the bands are often wrong for you

The bands were derived from mid-20th-century European adult data. They ignore muscle mass, ethnicity, age over 65 and pregnancy. A chart cannot see body composition.

Use the row, not the cell

The most useful information on a BMI chart is the healthy weight range for your height — for 1.75 m that is 56.7–76.3 kg. That range is a target, the single number is not.

When to ignore the chart entirely

Under 18, pregnant, post-surgery, in cancer treatment, or a competitive strength athlete. In each case a different metric applies.

Pair it with waist-to-height ratio

Divide waist by height. Under 0.5 is the goal at any BMI. This single extra number catches most of the risk BMI misses.

Sources & further reading

BIPM — The International System of Units (SI Brochure)
NIST — Guide for the Use of the International System of Units
WHO — Body weight & health guidance

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