How to calculate your BMI

The body mass index is the best-known indicator for assessing body size. It can be calculated in a few seconds and gives a useful first indication. But it also has important limits that you need to know so as not to draw hasty conclusions. This guide gives you the formula, interpretation, and necessary perspective.

Steps

1

Weigh yourself under the right conditions

Weigh yourself in the morning on an empty stomach, after using the bathroom, in your underwear. Always use the same scale on a hard, flat surface. A single weigh-in can vary by 0.5 to 1.5 kg from one day to the next — this is normal.

2

Measure your height accurately

Stand straight, barefoot, heels together against a wall. Use a rigid measuring tape or ask someone to measure. You lose 1-2 cm in height during the day due to disc compression — measure yourself in the morning for better consistency.

3

Apply the formula: weight (kg) / height (m)²

Divide your weight in kilograms by the square of your height in meters. Example: 75 kg / (1.75 m)² = 75 / 3.0625 = 24.5. It's a simple calculation that requires no special equipment or expertise — just a scale and a tape measure.

4

Interpret the result according to WHO categories

Under 18.5: underweight. 18.5-24.9: normal weight. 25.0-29.9: overweight. 30.0 and above: obesity. These thresholds are defined by the WHO for the general adult population. They do not account for muscle mass, age, or ethnicity.

What BMI measures (and doesn't measure)

BMI is a statistical indicator designed to assess populations, not individuals. It correlates weight and height to estimate overall health risk. It does not distinguish between fat mass and muscle mass: a rugby player with a BMI of 30 does not have the same risk profile as a sedentary person with the same BMI. It also doesn't account for fat distribution — visceral (abdominal) fat is more dangerous than subcutaneous fat.

BMI categories and their meaning

A BMI between 18.5 and 24.9 is associated with the lowest mortality risk in epidemiological studies. A BMI above 30 significantly increases the risk of type 2 diabetes, cardiovascular disease, and certain cancers. A BMI below 18.5 is associated with an increased risk of deficiencies, osteoporosis, and weakened immunity. These categories are screening tools, not diagnoses.

Limitations to keep in mind

BMI overestimates fat in muscular people and underestimates it in older adults who have lost muscle mass. WHO thresholds were defined based on Caucasian populations — the WHO recommends lower thresholds for Asian populations (overweight starting at 23). Waist circumference (> 94 cm for men, > 80 cm for women) is a better predictor of cardiovascular risk than BMI alone.

FoodCraft Tip

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The FoodCraft BMI calculator shows your result along with the WHO interpretation, category, and clear visual markers. You get full context, not just a number.

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Frequently asked questions

My BMI is 'overweight' but I exercise a lot, should I be worried?
Probably not. If you have significant muscle mass, your BMI will be high without reflecting excess fat. Supplement with a waist circumference measurement or body fat percentage for a more accurate view.
Is BMI reliable for children?
No, not with the adult formula. For children and adolescents, growth charts are used that account for age and gender. The calculation is different and so are the thresholds.
What is the 'ideal' BMI?
Studies show that the lowest mortality risk is between a BMI of 20 and 25. But the 'ideal' BMI also depends on your body type, age, and activity level. One number doesn't define your health.
Is BMI enough to assess my health?
No. BMI is just one indicator among others. Blood pressure, lipid profile, fasting blood glucose, and waist circumference provide a more complete picture. BMI is a starting point, not a conclusion.

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