> For the complete documentation index, see [llms.txt](https://emotiv.gitbook.io/epoc-flex-user-manual/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://emotiv.gitbook.io/epoc-flex-user-manual/cap/choosing-cap-size.md).

# Choosing the Cap Size

Specifying the right cap size is critical for ensuring the sensors are in the right place when taking measurements. Our supplier recommends measuring the head diameter in the horizontal circumference as shown in the image below.

![](/files/-LIeRtdImZWiD6VgzqX0)

Once you have the measurement for your test subjects, specify the closest size to the ones available, for example 54.5cm → 54cm,  59cm → 58cm, etc. If you need larger or smaller sizes, please contact support.