The RadChart in asp.net ajax is being rendered as an image and sent to the client. That means that when the browser gets a simple image with size 250x340 (as you have set it). There is no way that the server can know what is the size of this td while it is rendering the chart, that is, before the html has been sent to the client.
However, there is a way that you can achieve this - when the page has loaded on the client machine you can measure the td and do a postback to get the server to render a new image with the new size. You can see how this can be done here
- one of our code libraries. I have also attached a simpler project that resizes the chart after the initial load, however, we generally suggest using the approach with the ajax manager.
All the best,
the Telerik team
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