# The optimal cluster density and PhiX loading concentration for MiniSeq runs

The optimal raw cluster density range for a whole-genome library, such as PhiX, is 170-220k/mm2.

For a 100% PhiX run, Illumina recommends a loading concentration 1.4 pM to avoid over clustering the flow cell.

For further information, see [Cluster Optimization Overview Guide](https://support.illumina.com/downloads/cluster-optimization-overview-guide-1000000071511.html).

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