What is the 'number of items' limit?


When I submit a CDS API request, I get a message saying 'number of items' limit has been exceeded. What does that mean?

The same question, this message appears when I download the data on all pressure levels.


In order to manage the request load on the CDS system, a limit has been introduced on the number of 'items' which can be delivered by the CDS in a single user request (submitted either by the CDS web interface or by the CDS API).

This limit varies from dataset to dataset, as it depends on the granularity of the data served. For ERA5, 1 'item' corresponds to 1 variable on a (2D) field at 1 level at 1 timestep.

So a request for 2m temperature for 1 day would correspond to 1 (variable) x 1 (level) x 24 (hourly timesteps) = 24 'items'

Any request submitted to the CDS which is larger than the limit for that dataset will be rejected by the system, so you will need to modify you selection until it is smaller than the limit.

If you go to the "Download data" tab for a given dataset (e.g. ERA5), you can build a request interactively and you will get a warning if it exceeds the limit.

Please note that these limits can change over time in order to balance the load on the system.


Copernicus User Support team

That is very helpful, thanks Anabelle!