Fill it to the very top of the bottle. When you remove the bottling wand, the appropriate amount of head space will be there. It is almost like magic![]()
Just make sure you have an inch of headspace before capping. If you are not using a filling wand, you might overfill. I find that my filling wand leaves too much headspace, so I top up by touching the side of the bottle as I pull it out.
I do the same thing. When I remove the wand there is a lot of head space so I push it up against the inside of the bottle and fill it up a little more.