What Are the 5th, 50th, and 95th Percentiles Used for in Design?

The $5^{\text{th}}$, $50^{\text{th}}$, and $95^{\text{th}}$ percentiles help designers accommodate different body sizes within a target population. Designers generally use the $5^{\text{th}}$ percentile for reach or minimum dimensions, the $95^{\text{th}}$ percentile for clearance, and the range between them for adjustable products.

How Percentiles Work

Anthropometric data are measurements of human body dimensions, such as stature, hand width, or seated eye height. A percentile indicates the percentage of the sampled population whose measurement is equal to or below a stated value.

For example, a $95^{\text{th}}$-percentile male stature means that $95\%$ of males in the relevant population are that height or shorter. It does not mean that one person is in the same percentile for every body measurement.

For a control panel, designing the maximum reach distance for a $5^{\text{th}}$-percentile user allows most larger users to reach it as well. In contrast, a doorway based on a $95^{\text{th}}$-percentile stature provides clearance for most users.

An adjustable office chair may span from the $5^{\text{th}}$-percentile user to the $95^{\text{th}}$-percentile user, accommodating approximately $90\%$ of the target population. The excluded extremes may require specialized designs.

A common misconception is that designing for the $50^{\text{th}}$ percentile fits most people. It fits the median measurement, but it may fit relatively few users well when several body dimensions are involved.

IB Exam Technique

For A1.1 Ergonomics, identify the relevant anthropometric measurement and justify the chosen percentile. Link small-user reach to the $5^{\text{th}}$ percentile, large-user clearance to the $95^{\text{th}}$, and inclusive adjustment to the $5^{\text{th}}$-to- range.