# What is default similarity in Elasticsearch 5

**URL:** <https://discuss.elastic.co/t/what-is-default-similarity-in-elasticsearch-5/68440>\
**Category:** Elasticsearch\
**Created:** [December 8, 2016, 1:57pm UTC](https://discuss.elastic.co/t/what-is-default-similarity-in-elasticsearch-5/68440 "2016-12-08T13:57:58Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![svarup](https://avatars.discourse-cdn.com/v4/letter/s/ee59a6/32.png) [@svarup](https://discuss.elastic.co/u/svarup)\
**Post date:** [December 8, 2016, 1:57pm UTC](https://discuss.elastic.co/t/what-is-default-similarity-in-elasticsearch-5/68440/1 "2016-12-08T13:57:58Z")

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I have been trouble to find what is the default similarity in Elasticsearch 5  
is BM25 or Classic Lucene IF/IDF?

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**Author:** ![colings86](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/colings86/32/44960_2.png) [@colings86](https://discuss.elastic.co/u/colings86)\
**Post date:** [December 8, 2016, 2:06pm UTC](https://discuss.elastic.co/t/what-is-default-similarity-in-elasticsearch-5/68440/2 "2016-12-08T14:06:49Z")

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The default in 5.0 is BM25. See [https://www.elastic.co/guide/en/elasticsearch/reference/5.0/similarity.html](https://www.elastic.co/guide/en/elasticsearch/reference/5.0/similarity.html) for more details

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<div class="post-metadata">

**Author:** ![svarup](https://avatars.discourse-cdn.com/v4/letter/s/ee59a6/32.png) [@svarup](https://discuss.elastic.co/u/svarup)\
**Post date:** [December 8, 2016, 2:22pm UTC](https://discuss.elastic.co/t/what-is-default-similarity-in-elasticsearch-5/68440/3 "2016-12-08T14:22:23Z")

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so if I want to use TF/IDF then am I correct with below code?

'similarity' =\> [  
'default' =\> [  
'type' =\> 'classic',  
],  
],

is **classic** point out to TF/IDF?

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<div class="post-metadata">

**Author:** ![colings86](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/colings86/32/44960_2.png) [@colings86](https://discuss.elastic.co/u/colings86)\
**Post date:** [December 8, 2016, 2:34pm UTC](https://discuss.elastic.co/t/what-is-default-similarity-in-elasticsearch-5/68440/4 "2016-12-08T14:34:25Z")

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Yes `classic` indicates that you want to use TF/IDF. information on setting the default similarity can be found here: [https://www.elastic.co/guide/en/elasticsearch/reference/5.0/index-modules-similarity.html#default-base](https://www.elastic.co/guide/en/elasticsearch/reference/5.0/index-modules-similarity.html#default-base)

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<div class="post-metadata">

**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\
**Post date:** [January 5, 2017, 2:35pm UTC](https://discuss.elastic.co/t/what-is-default-similarity-in-elasticsearch-5/68440/5 "2017-01-05T14:35:13Z")

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