Dynamic text question

What is wrong with this. I have a dynamic text field on the stage, instance name contentLength. I get this error: 1067: Implicit coercion of a value of type Number to an unrelated type String.

import flash.display.*;
import flash.events.*;
import flash.text.TextField;

var mcHolder:MovieClip = new MovieClip();
mcHolder.width = 200;

contentLength.text = mcHolder.width;