> For the complete documentation index, see [llms.txt](https://knowledge.illumina.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://knowledge.illumina.com/instrumentation/general/instrumentation-general-reference_material-list/000001511.md).

# Cluster density guidelines for Illumina sequencing platforms using non-patterned flow cells

Cluster density is an important factor in optimizing data quality and yield. The following table lists the recommended raw cluster densities for balanced libraries (such as PhiX):

![](https://761066130-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FGM9W2DuBTgEXv1ClCm8H%2Fuploads%2Fgit-blob-1affeb5f917a8687fba63ee17c4cb1e0ddb047e8%2Fimage1.jpg?alt=media\&token=881b84bc-c463-42ab-8c49-91b1cf3d8e2b)

The iSeq 100, MiSeq i100 Series, NextSeq 1000/2000, NovaSeq 6000, and NovaSeq X Series systems utilize patterned flow cells. This results in a fixed cluster density, even if all nanowells are not occupied. In these systems, monitoring the Cluster Pass filter (%) is a better measure of potential cluster occupancy.

See the following for further details:

* [Plotting %Occupied by %PF to optimize loading for the NovaSeq 6000 and X, MiSeq i100, and iSeq 100](/instrumentation/general/instrumentation-general-reference_material-list/000002308.md)
* [Calculating Percent Passing Filter for Patterned and Nonpatterned Flow Cells](/instrumentation/general/instrumentation-general-reference_material-list/000006309.md)

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| *For any feedback or questions regarding this article (Illumina Knowledge Article #1511), contact Illumina Technical Support* [*techsupport@illumina.com*](mailto:techsupport@illumina.com?subject=Question%2FFeedback%20Regarding%20Illumina%20Knowledge%20Article%20#000001511%20-%20Instrumentation%20\&body=Dear%20Illumina%20Technical%20Support,%0D%0A%0D%0A)*.* |


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