Hop retention

[DRB]

How much of the brew on average is lost to hops after boil.I am doing a 15lt batch,so will be boiling about 22lt,it's just that i'll be using 80g of hops in a smaller brew.

[oblivious]

Some people do a hop sparge to recover the lost wort

[tubby_shaw]

Some people do a hop sparge to recover the lost wort

I'm one of those people
I find the hop sparge solves a few problems.
A. As I cool to 20 C or so to achieve a good cold break sparging the hops with boiling water will increase the temperature closer to the ideal for pitching the yeast.
B. I can top up with hop sparge to the desired volume.
C. Being a tight Yorkshireman I don't leave as much of the fermentables behind in the hops

[DRB]

So the more hops you use the more wort you'll lose.

[tubby_shaw]

So the more hops you use the more wort you'll lose.

Yup
But all you have to do is add a little more malt initially to compensate

[Aleman]

The 'conventional wisdom' is that 1Kg of hops displaces 1L of wort and ABSORBS 15L. Of course then you have losses of stuff retained in teh pipework etc.