Amazon Polly
Developer Guide

Limits in Amazon Polly

The following are limits to be aware of when using Amazon Polly.

Supported Regions

For a list of AWS Regions where Amazon Polly is available, see AWS Regions and Endpoints in the Amazon Web Services General Reference.


  • Throttle rate per account: 100 transactions (requests) per second (tps) with a burst limit of 120 tps.

    Concurrent connections per account: 90

  • Throttle rate per operation:








    Any 2 transactions per second (tps) from these operations combined.

    Maximum allowed burst of 4 tps.



    80 tps with a burst limit of 100 tps


    80 tps with a burst limit of 100 tps

Pronunciation Lexicons

  • You can store up to 100 lexicons per account.

  • Lexicon names can be an alphanumeric string up to 20 characters long.

  • Each lexicon can be up to 4,000 characters in size. (Note that the size of the lexicon affects the latency of the SynthesizeSpeech operation.)

  • You can specify up to 100 characters for each <phoneme> or <alias> replacement in a lexicon.

For information about using lexicons, see Managing Lexicons.

SynthesizeSpeech API Operation

Note the following limits related to using the SynthesizeSpeech API operation:

  • The size of the input text can be up to 3000 billed characters (6000 total characters). SSML tags are not counted as billed characters.

  • You can specify up to five lexicons to apply to the input text.

  • The output audio stream (synthesis) is limited to 10 minutes, after which, any remaining speech is cut off.

For more information, see SynthesizeSpeech.


Some limitations of the SynthesizeSpeech API operation can be bypassed using AWS Batch or other services. For more information on AWS Batch, see What Is AWS Batch?

Speech Synthesis Markup Language (SSML)

Note the following limits related to using SSML:

  • The <audio>, <lexicon>, <lookup>, and <voice> tags are not supported.

  • <break> elements can specify a maximum duration of 10 seconds each.

  • The <prosody> tag doesn't support values for the rate attribute lower than -80%.

For more information, see Using SSML.