Originally Posted by Duffman53
Well, this reply is around six years after the initial post but thought I would add this for newbies...
There is a tool called a refractometer that can gaugethe abv of your beer without taking any gravity readings. The neatest thing about it is that it is that you only use a few drops of beer (maybe a spoonful...) instead of wasting six to eight ounces on two occasions to take your readings with a hydrometer.
Unfortunately, refractometers are quite expensive. I believe they run around $60.
I didn't want to take part in a zombie thread, but this isn't quite right.
A refractometer takes a gravity reading, just like a hydrometer does. It won't magically give you an ABV reading without a starting gravity. It IS true that a refractometer only requires a drop or two of wort to take a reading.
One downside to a refractometer is that alcohol presence skews its reading. There are online calculators that will tell you the correct reading with alcohol present, but they require you to have a SG reading already.
As for a late, late, late response to the OP's question...with extract brewing, as long as you got your volume measurements correct, your OG should be exactly what a recipe calls for. If you made up the recipe, there are several tools available online that will calculate it for you.