Can't get my volumes right!

[Battleaxe]

I've never managed to hit my post boil volume bang on! I've tried upping my sparge incrementally until today I ended up with 5lts of wort instead of 4.5l!!

I had been using a boil volume of 7ish lts and decided to up this to 8lts today and ended up with 5lts of 1.032 wort meaning my final ABV will be 3.2% ish instead of 3.6 I was aiming for...

I brew small batch AG 4.5lt batches usually with around 1kg grain bill.

I've worked out my mash tun dead space is 200ml and I've assumed the grain will absorb 1lt of water, so I mash with 2lts of water and expect 900ml from my first run I then sparge with 7lts of water to achieve a boil volume of 8lts as boil off volume was my only unknown so should I aim for 6.5 lts sparge next time or have I missed something?

[ManseMasher]

I work on 2.5l for every kilo of grain. The only way to nail your boil off is to measure the liquid pre and post boil, that way you can accurately work out your desired starting quantity and therefore how much sparging you need to do.

[Goulders]

I think with such a small batch volume there is little room for error in boil off rates etc, so you will struggle to nail it every time

[Battleaxe]

Well I started with 8lts of boil and ended with 5lts so a boil off average being 3lts means next time I should aim for a 7.5lt boil... We shall see I brew whenever I've got a spare 4hrs so it won't be long!