In your case the problem comes from the fact that you have more than one element on the web page, which change their height on the client until the page is fully loaded. Therefore, the RadGrid height depends on other control height positioned on the top of the page.
. An easier solution will be to use RadSplitter with two RadPanes - the top panel could contain the other controls, while the bottom one - the RadGrid. In this case you can keep the RadGrid's 100% height.
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