There are two possible approaches.
The first one is just informative - add a label around the RadUpload
instance, which will display the maximum allowed size.
The other approach is to use the client-side file size checking
approach. Please note, that the latter depends on the asynchronous progress update Ajax calls and some the data gets uploaded before the client-side event is triggered. That means that on localhost validation might not occur if uploading relatively small files (e.g. <5MB).
You can use both the approaches to make best client experience.
I hope that helps.
the Telerik team
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