# Picking values for --p-min-length and --p-max-length in qiime feature-classifier extract-reads

**URL:** https://forum.qiime2.org/t/picking-values-for-p-min-length-and-p-max-length-in-qiime-feature-classifier-extract-reads/20912
**Category:** User Support
**Tags:** feature-classifier
**Created:** [September 28, 2021, 8:24am UTC](https://forum.qiime2.org/t/picking-values-for-p-min-length-and-p-max-length-in-qiime-feature-classifier-extract-reads/20912 "2021-09-28T08:24:18Z")
**Posts on this page:** 1
**Showing post:** 4

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### Author: ![Deni\_Ribicic](https://forum.qiime2.org/user_avatar/forum.qiime2.org/deni_ribicic/32/17065_2.png) [@Deni\_Ribicic](https://forum.qiime2.org/u/Deni_Ribicic)
#### Post date: [September 29, 2021, 12:43pm UTC](https://forum.qiime2.org/t/picking-values-for-p-min-length-and-p-max-length-in-qiime-feature-classifier-extract-reads/20912/4 "2021-09-29T12:43:36Z")

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Hi Kevin,

I think your assumption regarding the amplicon length is correct. But for training the classifier I wouldn't go with too tight interval params. You may be risking removing biologically relevant sequences due to differences in 16S rRNA gene in different prokaryotic groups (as you mention also in your previous post).

I am pretty comfortable with `--p-min-length 400` and `--p-max-length 500` as this gives me enough error margin, and certainty that I am recapturing relevant sequences and excluding some larger artefacts 🙂

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