Last Updated: 16 June 2015

Table of Contents

This is an aggregation of the limits imposed on various components of the Heroku platform. It lists only the limits (number of connections, for example) not the features (this database plan has that capability).

Limits exist for several reasons. Sometimes limits are present because of how the underlying platform is constructed: for example, Heroku stores only 1500 lines of log history (the rest being available via a logging add-on). Sometimes limits are present because they enforce good citizenship: for example, you can’t make more than 2400 API requests an hour.

Each limit here is documented with a link to the source document that documents the limit, and which provides a lot more context to the limit.


Log history limits

Heroku only stores the last 1500 lines of log history. If you’d like to persist more than 1500 lines, use a logging add-on or create your own syslog drain.



You can have up to 5 drains on any given app.

Line length

Lines generated by dynos that exceed 10000 bytes are split into 10000 byte chunks w/o extra trailing newlines. Each chunk is submitted as a separate log line.



HTTP timeouts

HTTP requests have an initial 30 second window in which the web process must return response data (either the completed response or some amount of response data to indicate that the process is active). Processes that do not send response data within the initial 30-second window will see an H12 error in their logs.

After the initial response, each byte sent (either from the client or from your app process) resets a rolling 55 second window. If no data is sent during this 55 second window then the connection is terminated and a H15 error is logged.


HTTP response buffering

The router maintains a 1MB buffer for responses from the dyno per connection.


HTTP request buffering

When processing an incoming request, a router sets up an 8KB receive buffer and begins reading the HTTP request line and request headers. Each of these can be at most 8KB in length, but together can be more than 8KB in total. Requests containing a request line or header line longer than 8KB will be dropped by the router without being dispatched.



Dyno memory

Different dyno sizes offer differ amounts of maximum RAM:

  • free, hobby and standard-1x have 512MB
  • standard-2x has 1024MB
  • performance has 6GB


Dyno memory and restarts

If the memory size of your dyno keeps growing until it reaches five times its quota (for a standard-1x dyno, 512MB x 5 = 2.5GB) or two times its quota for performance dynos, the dyno manager will restart your dyno with an R15 error.


Attached one-off dyno timeout

Connections to one-off dynos will be closed after one hour of inactivity (in both input and output). When the connection is closed, the dyno will be sent SIGHUP. This idle timeout helps prevent unintended charges from leaving interactive console sessions open and unused.


Detached one-off dyno timeout

Detached one-off dynos are cycle every 24 hours. As a result, a one-off dyno will run for a maximum of 24 hours


Concurrent one-off dynos

There are different limits that apply depending on whether the Heroku account is verified or not.

If the account is not verified, then it cannot have more than 3 one-off dynos of type free or hobby running concurrently. Accounts that aren’t verified can’t create one-off standard or one-off performance dynos.

For verified accounts, no more than 5 performance one-off dynos can run concurrently.

Contact sales to raise this limit for your application.


Config vars

Config var data (the collection of all keys and values) is limited to 16kb for each app.


Boot timeout

The web process in a dyno may not take more than 60 seconds to bind to its assigned $PORT.

Contact support to increase this limit to 120 seconds on a per-application basis. In general, slow boot times will make it harder to deploy your application and will make recovery from dyno failures slower, so this should be considered a temporary solution.


Exit timeout

When a dyno is killed or restarted, the processes within the dyno have 10 seconds in which to exit on receiving a SIGTERM. The process is sent SIGKILL to force an exit after this 10 seconds.


Dyno restart limits

Heroku’s dyno restart policy is to try to restart crashed dynos by spawning new dynos once every ten minutes. This means that if you push bad code that prevents your app from booting, your app dynos will be started once, then restarted, then get a cool-off of ten minutes. In the normal case of a long-running web or worker process getting an occasional crash, the dyno will be restarted instantly without any intervention on your part. If your dyno crashes twice in a row, it will stay down for ten minutes before the system retries.


Dyno scale

The free and hobby dyno types only support a maximum of one dyno running per process type. Additionally, applications using a free dyno type are limited to a maximum of two concurrent running dynos.

By default, a process type can’t be scaled to more than 100 dynos for standard-1X or standard-2X sized dynos. A process type can’t be scaled to more than 10 dynos for performance dynos.

Contact sales to raise this limit for your application.


Processes / threads

The maximum number of processes/threads that can exist in a dyno at any one time depends on dyno type:

  • free, hobby and standard-1x dynos support no more than 256
  • standard-2x dynos support no more than 512
  • performance dynos support no more than 32768

These limits include all processes and threads, whether they are executing, sleeping or in any other state. Note that the dyno counts threads and processes towards this limit. For example, a standard-1x dyno with 255 threads and one process is at the limit, as is a dyno with 256 processes.



Git repos

Users are limited to a rolling window of 75 requests to Heroku Git repos per hour, per app, per user.

The uncompressed size of a checkout of HEAD from the repo, combined with the size of restored submodules, cannot exceed 1 GB.


Slug size

Your slug size is displayed at the end of a successful compile. The maximum slug size is 300MB; most apps should be far below this limit.


Slug compilation

Slug compilation is limited to 15 minutes.


Heroku Postgres

Dataclips row limits

Dataclips may return up to 100,000 rows.


Dataclips query limit timeout

Dataclips will cancel queries after 10 minutes.


Standard, Premium, and Enterprise tier


Hobby tier

  • Enforced row limits of 10,000 rows for dev and 10,000,000 for basic plans
  • Maximum of 20 connections
  • No in-memory cache



Heroku API limits

Calls to the Heroku API is limited to a rate of at most 2400 calls per hour.



Maximum number of applications

Unverified accounts can create at most 5 apps. Verified accounts can create no more than 100 applications.


Maximum number of SSH keys

All accounts may have a maximum of 50 SSH keys associated with their accounts. If you need more than this you should look into using the Build API