It is not only about height, but also about terrain closure rate. That's what you see by looking at the end of the runway. After the 10 feet call has passed, at your guessed 0 feet, you want the terrain closure rate to be (nearly) 0.
You can only guess the aircrafts height if you're looking around, or down over the nose, but then you don't see the closure rate anymore.
You should be looking at the end of the runway, to see what the aircraft is doing. When you get more experienced, you will be able to do it with height/looking nearby, i.c.w. muscle memory.
Hope this helps...
edit: typo