Help with OG Calculation (Math Deficient)

Due to the size of my primary kettle (#1) I needed to dump some of the sparge into a second kettle. So my brew day ended with the 2 brew kettles at different volumes and starting gravities:

Kettle 1 - 3.5 gallons @ 1.081
Kettle 2 - 1.5 gallons @ 1.042

The entire wort was all tossed in a 5 gallon glass carboy. Without pulling a sample, can anyone calculate the actual SG of this beer? Or at least ballpark it?

I was shooting for 1.066 with this beer.

It should be a weighted average: 81*(3.5/5) + 42*(1.5/5) = 69 (1.069)

81 x 3.5 = 283.5
42 x 1.5 = 63
283.5 + 63 = 346.5
346.5 / 5 = 69.3
69.3 = 1.069

This is assuming your gravity readings were temperature corrected.

cp

The above math looks good to me and if not it is prob close enough for beer!

http://www.rooftopbrew.net/abv.php

Awesome! Thanks for the help.