Hit OG, but low on final volume??

Hey guys, I just finished brewing up the recipe for the northern brewer kit called Sinistral Warrior IPA. The OG is supposed to be 1.065 and I hit that right on the money. Could not be more on point. However, I swear that by looking at my fermenter, I only have about 4 gallons in my 6.5 gallon carboy. I mean the thing looks just over half-full, yet I somehow managed to hit my OG on the money. How could this have happened? Or am I just used to brewing bigger batches, and the 5 gallons in my carboy just looks smaller to me? Sooo perplexed, but happy to be hitting my OG readings finally...

All grain or extract?

If AG maybe your efficiency was low and boil off was high.

All grain...and I just used my barley crusher for the first time so idk about efficiency but this carboy looks half empty

Well, you may have less collected wort due to: 5 oz. of hops (absorption), evaporation rate of boil that particular day (dry weather), length of boil?, etc. Also, a different grind setting could effect your mash efficiency. Would not be suprised if your LHBS has a favorite setting which is not neccessarily the 'standard' setting.

To be sure about your volume, you could always measure the circumference of the carboy and divide by 6.28 (2xPi) to get the radius. Then measure the height of the wort in the carboy and multiply it by 3.14 x radius^2 to get volume in cubic inches. Dived by 231 cu.in/gal to get gallons.

Granted your ballpark volume here would be a tad more accurate if you could subtact out the thinckness of the glass on the radius & height, but it should be pretty close. (not to mention the taper at the bottom of the carboy)..

As long as you have a tasty beer at the end, all is good!
--Chris