# Changing ring dimension by mult\_depth value

**URL:** <https://openfhe.discourse.group/t/changing-ring-dimension-by-mult-depth-value/1392>\
**Category:** FHE Questions\
**Created:** [June 30, 2024, 7:16pm UTC](https://openfhe.discourse.group/t/changing-ring-dimension-by-mult-depth-value/1392 "2024-06-30T19:16:31Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![evgen](https://avatars.discourse-cdn.com/v4/letter/e/85f322/32.png) [@evgen](https://openfhe.discourse.group/u/evgen)\
**Post date:** [June 30, 2024, 7:16pm UTC](https://openfhe.discourse.group/t/changing-ring-dimension-by-mult-depth-value/1392/1 "2024-06-30T19:16:31Z")

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There is some context why/how ring dimesion changed by increasing mult\_depth value. If i increment mult\_depth from 1 to 4 my ring dimesion is 16384. And after 4 to 7 is 32768. After 7 i get approximation error

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**Author:** ![andreea.alexandru](https://yyz1.discourse-cdn.com/flex031/user_avatar/openfhe.discourse.group/andreea.alexandru/32/378_2.png) [@andreea.alexandru](https://openfhe.discourse.group/u/andreea.alexandru)\
**Post date:** [July 1, 2024, 7:55am UTC](https://openfhe.discourse.group/t/changing-ring-dimension-by-mult-depth-value/1392/2 "2024-07-01T07:55:44Z")

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The mult\_depth (along with firstModSize, scalingModSize etc) determines the ciphertext modulus. If you set a security level (by default it is HEStd\_128\_classic), then a ring dimension is chosen to achieve this security level given the ciphertext modulus, according to the tables in [http://homomorphicencryption.org/wp-content/uploads/2018/11/HomomorphicEncryptionStandardv1.1.pdf](http://homomorphicencryption.org/wp-content/uploads/2018/11/HomomorphicEncryptionStandardv1.1.pdf).

Please watch the introductory webinars [here](https://www.openfhe.org/webinars/) in order to learn more about these concepts.