Regex to limit string length for strings with new line characters

Looks like a simple task - get a regex that tests a string for particular length: ^.{1,500}$

But if a string has "\r\n" than the above match always fails!

How should the correct regex look like to accept new line characters as part of the string?

I have a <asp:TextBox TextMode="Multiline"> and use a RegularExpressionValidator to check the length of what user types in.

Thank you, Andrey