What does a BMI of 51 mean?

A BMI of 51 explained

Is a BMI of 51 healthy?

On the standard scale used by the World Health Organization^[1], a BMI of 51 is obese — so it is not in the healthy range. This is in the obese range. Obesity is associated with an increased risk of conditions including type 2 diabetes, heart disease and some cancers, and the statistical risk tends to rise as BMI increases.

Keep in mind that BMI is a screening tool, not a diagnosis^[2]: it can over- or under-estimate body fat for muscular, athletic, or larger- and smaller-framed people, and it is judged differently once age and sex are taken into account (see below). For advice about your own health, talk with your doctor.

How a BMI of 51 is classified by age and sex

The standard BMI scale is the same for everyone, but body composition changes with age. The table below shows how a BMI of 51 is classified for each age group and sex, using the redefined cut-offs from a 2015 NCBI study^[3].

What weight gives a BMI of 51?

A BMI of 51 is a different weight at each height. To reach this BMI you would weigh:

Nearby BMI values

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What is BMI?

BMI (Body Mass Index) is a person's weight in kilograms divided by the square of their height in meters. For most people it is a good predictor of health problems linked to excess or lack of weight. It is also known as Quetelet's index.

BMI on its own does not measure body fat directly, so it can be misleading for very muscular or large-framed people. Our scale is better than a standard BMI chart because it factors in both age and sex.

Standard BMI Chart (WHO)

This table defines the fixed BMI ranges still widely used to compare populations.

Modified BMI Chart (by age and sex)

A 2015 NCBI study adjusted the overweight and obese limits to reflect changes in body composition with age. These redefined thresholds drive the table at the top of this page.

Important note

This calculator is not a source of clinical guidance. BMI is only an indicator of body fatness and does not apply to athletic or very muscular builds, nor to children. Do not take important health decisions based on this or any other web tool. Discuss weight loss or diet changes with your doctor or nutritionist.

References:

1. World Health Organization — Obesity and overweight (fact sheet)
2. Centers for Disease Control and Prevention (CDC) — Adult BMI Categories
3. The need to redefine age- and gender-specific overweight and obese body mass index cutoff points (NCBI, 2015)

BMI categories follow WHO and CDC guidance; the age- and sex-adjusted ranges follow the 2015 NCBI study. Last updated: Sep 2026.

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