Maximum value of maxRequestLength?

These two settings worked for me to upload 1GB mp4 videos.

<system.web>
    <httpRuntime maxRequestLength="2097152" requestLengthDiskThreshold="2097152" executionTimeout="240"/>
</system.web>
<system.webServer>
    <security>
        <requestFiltering>
            <requestLimits maxAllowedContentLength="2147483648" />
        </requestFiltering>
    </security>
</system.webServer>

Maximum is 2097151, If you try set more error occurred.

2,147,483,647 bytes, since the value is a signed integer (Int32). That's probably more than you'll need.

As per MSDN the default value is 4096 KB (4 MB).

UPDATE

As for the Maximum, since it is an int data type, then theoretically you can go up to 2,147,483,647. Also I wanted to make sure that you are aware that IIS 7 uses maxAllowedContentLength for specifying file upload size. By default it is set to 30000000 around 30MB and being an uint, it should theoretically allow a max of 4,294,967,295