Wasn't even 4 inches. Sky's agenda involves showing the incident from a camera on the half-way line and it looks way out from that angle. But the law says that the whole of the ball has to be over the line, which means the full diameter of the ball, not just the bit that's touching the ground. If any part of the whole diameter is intersecting the line, it's in play.
When you look at it using a view directly down the goal-line it's much less clear and, at worst, it's millimetres out. It might even be just in as a small part of the ball at the extremity of its diameter might be over the line. But that's from studying a still photo and blowing it up and it's still not 100% clear. So if it's almost impossible to tell from that, how is anyone supposed to know from one view in real-time? And if they're not 100% sure then they can't give it.
Don't fall into Sky's trap.