Boil off percentage

I'm just curious what you guys are using as your boil off percentage, if your using a keggle, or i guess any 15 gallon brew pot should be similar.
the default in beersmith is 9%, which for me is a bit low, i tried 12, and i think that's too high.
I'm going to try 11 this time, unless i get some sort of overwhelming response here.
Thanks

Joe

It is really going to be trial and error (imo). The temperature outside and how vigourous your boil is play a part too. Good luck... I still suck at figuring this out.

The best thing to do is make a calibrated brew stick to measure your volumes pre boil and post boil for an exact measure.

Evaporation/boil off will be different depending on the conditions, cold dry is usually more and hot humid is usually less. You will have some variation also depending upon the depth and surface area of you Bk. I use a 10g BK that is as wide as tall and on average lose 1-1.25g per hour

Wort also shrinks as it cools so you need to calculate your shrinkage as well. It may take you a couple batches of measuring to get your average.

I actually created 3 different equipment profiles depending upon the season with the average appropriate numbers plugged in based on observed/measured results

I did read that the boil off is a consant, so when I brew tomorrow I'm going to measure the exact boil off to use as a guesstimate.