calculating OG

So, I used a recipe formulator (beer recipator) and calculated an OG of 1.066. When I brewed, I took a reading from the kettle, then after racking to the primary I had to top-off with 0.75 gallons of water.

Reading was at 1.072. So, is this formula correct for calculating real OG?

[4.25(1.072) + 0.75] / 5

because that equates to 1.0612, which is a bit lower than expected OG.

I used 7 lb of DME in a 6 gallon boil. I did leave some behind in the kettle, for the trub. Is this where my missing gravity is?

Beersmith comes up with 1.061 so I'd say your math is pretty dead on. I'm assuming your doing a 5 gallon batch. It sounds like you left...lets say a half gallon of wort in your pot and then added .75 gallons of water.... That would lower your OG. I usually just dump everything into the primary and then worry about top-off. Either way... the beer will come out fine. .005 won't be a deal breaker...

I do the same as Hammy, especially when I'm doing an extract brew. No real reason to worry about leaving much behind in the kettle. I just pour it all through a large kitchen strainer to get most of the hop gunk out. It's not like you're having a ton of hot break from extract and some cold break is good for the ferment if you're doing ales.

I did probably leave 1/2 gallon. I have one of those funnels with a fine mesh, and it got clogged pretty early on with hop material, and so I took the funnel out and siphoned straight into the carboy. I didn't want to have orange peel and trub material in the primary for a month, so i stopped it early.

i just bought a cane screen, so hopefully I can pull more out next time. Thanks!

I make 6 gal batches, with a 5 gal boil, and add 1 gal to the primary. I always seem to come up short on my OG. I would like to be able to measure the OG in the kettle, and account for the added gallon of water. That way I can add some more DME to get it up if necessary. So my math says that 1 of 6 gallons is 17%. So I can assume that the OG needs to be 17% higher? So lets say my OG should be 1.068 for a 6 gal recipe. Then, my 5 gal wort should be 68(1.17) or 1.079.... Does this seem right guys?

The easiest way? Use software like Beer Smith and enter a recipe for 6 gallons. Then change the batch volume to 5 gallons and leave everything else the same. That should tell you what your OG should be if you finish your boil with 5 gallons and top up with a gallon of water.