> For the complete documentation index, see [llms.txt](https://emotiv.gitbook.io/flex-2.0-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/flex-2.0-user-manual/flex-cap/choosing-the-right-flex-cap.md).

# Choosing the Right FLEX Cap

Choosing the right FLEX Cap for your study is essential for achieving accurate EEG measurements. 

To choose the right size of FLEX Cap for your participant, measure their head circumference, as shown in the image below. Once you have their measurement, choose a FLEX Cap from the range of sizes available — 54cm, 56cm, and 58cm sizes (whichever size is closest to their head circumference). 

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![](https://lh7-us.googleusercontent.com/BGBQxPKJCNpYBt2kTxMaPCIO3g9EjynElLEsMS63jdNPkg6KEDMlN8TCAE3fB89WRf4II8rbnLqzBRhC9t90TSXCsDDTX2DDmUIHDvmBc_0MtBzJaZEHGin2fGYOWBOt0Gp0xea4Anhw1WRdp24sP4I)