how much does og increase/gallon evaporated

I just finished NB Caribou Slobber BIAB and I forgot to take OG reading before I put my wort in fermenter. I can find a calculator for temperature difference but not one for volume difference.

Is there a rule of thumb or formula for OG increase/gallon evaporated.

My pre boil og was 1.050 at 60 degrees with 7 gallons. My final volume was 5 gallons.

I feel good about hitting the OG per NB recipe at 1.052. My competitive personality wants to know how close I really am.

Thanks for your help.

Pre-boil gravity is 1.050 for 7g. That's 50 points per gallon * 7, or 350 points.
Post-boil volume was 5g, so divide the 350 points by 5 = 70, which translates into an OG of 1.070
That assumes you didn't spill anything, you transferred everything into the fermenter, your pre boil gravity was correct, and your volumes were correct.
Assuming you made the AG version, you would have to get 93% mash lauter efficiency to get 7g pre boil at 1.050. That is a very high efficiency for a homebrewer.

-a.

Thanks for the formula ajf. I am using a kit hydrometer so I doubt my numbers are that accurate. Can't wait til santa brings the refractometer. I am glad I am in the ballpark. Nb gives grain bill assuming 70% efficiency.

Maybe the higher original gravity comes from higher efficiency than 70%. Thus I am converting more grain.

I like to think that is the case instead or a bad hydrometer.

I may be hitting a little higher efficiency than 70% but don' t think im near 93%.

i don't know if you got your answer, but it goes like this:

if you started with 1.050 SG at 6 gallons, you take the last two digits (50)

50 SG * 6 gal is the same as
54.54 SG * 5.5 gal (1.054 SG)
60 SG * 5 gal (1.060 SG)
66.66 SG * 4.5 gal (1.066 SG)]
etc.

Perfect application for a slide rule!

Set the cursor to the gravity (50) on the D scale, bring the number of gallons (7) on the CI scale under the cursor -then just move the cursor to whatever number of ending gallons you please on the CI scale and instantly read the new gravity on the D scale. Faster than using a calculator!