Have you tried to limit the amount of text users can input in a SharePoint form? If you have, maybe you've found, as I have, that it's not quite as easy as I thought it would be. If you're in the browser and add a new column to your form, choose "Single line of text" and you have the "Maximum number of characters:" field available right there. Ok, easy enough. However, if you choose "Multiple lines of text" you no longer have the "Maximum number of characters:" field. So, what do I now? Good question. This is what I've done and feel free to let me know if there is a better way.

You'll have to create a custom form in our best friend, SharePoint Designer. (I'm not going to cover how to create a new custom form and link it to the list you want as I'm sure that's covered elsewhere). When you add your Multiple lines of text field to the page it gets formatted as a List Form Field

If you check the Tag Properties you'll notice there is no property for limiting the number of characters. No problem, we'll just change the format of this field to a Multiline Text Box

Now that it's formatted as a Multiline Text Box, the MaxLength property becomes available in the Tag Properties. Set the character limit and you're good to go, right?

Not so fast. If you check the form in the browser, you'll notice you can still input as many characters as you want – the MaxLength property has no effect. What's going on, why didn't that work? That's the same question I asked. This happens because the multiline text box is rendered in the browser as a "Text Area" which does not support the maximum length property. I know what you're thinking, "that would have been nice to know before I changed all 150 fields to Multiline text boxes," tell me about it.

Here's what I found that works. I didn't come up with it on my own, here's where I found it: http://community.workflowgen.com/kb/how-can-i-set-the-maximum-length-of-a-multi-line-text-box-in.html

How can I set the maximum length of a multi-line text box in a web form?

Restricting the length of text on a Multi line textbox is not supported by the standard ASP.NET Web control. This can be done by adding the following Javascript function in your ASPX page.

1. Add a javascript:

At the top of your ASPX page you will see the following tag </ head > . A dd the following code under this tag:

<script language="javascript" type="text/javascript">function Count(text,long)
{
    var maxlength = new Number(long); // Change number to your max length.
    if (text.value.length > maxlength){
        text.value = text.value.substring(0,maxlength);
        alert(" Only " + long + " characters");
    }
}
</script>

2. Change your text controls on your ASPX page

On every multi-line text box where you would like to control the length, add the following code to the asp text box control.
onKeyUp="Count(this,300)" onChange="Count(this,300)"

Your original text control before adding this code:
<asp:TextBox ID="TESTDATA" runat="server" TextMode="MultiLine"></asp:TextBox>

After adding the code:
<asp:TextBox ID="TextBox1" runat="server" onKeyUp="Count(this,300)" onChange="Count(this,300)" TextMode="MultiLine"></asp:TextBox>

I actually added the javascript to the masterpage, but it worked for me. Here's what happens:

That's what I'm talking about.