Extra water in boil = low og?

[justonemore]

I just got done with my 2 batch ever, an Imperial Blonde Ale from BB. The kit said to boil 2.5 gallons, but I have read and been told by more than one person to do as big of a boil as possible.
Well I did a 4 gallon boil and everthing looks good but my og was just a little low. I made sure it was stirred good and only had to add back about 1.75 gallons to bring it up to just a tick over 5 gallons.
The kit said 1.067-1.071 and i came in at 1.062 corrected for temp. Like i said i know that is fine and i am not worried about anything, just trying to soak up a little knowledge from the masters here.

 

[turtleboy3737]

final volume is what matters.

details:
sg is pretty much a measure of sugars in the water. Your malt extract is your sugars.
less water with the same sugars is higher sg, in your case you may have topped off with too much water(maybe you didnt boil off .75?) which brought your sg down.

 

[Teromous]

That's correct, the more water you add the lower the gravity will be. As the water vapors leave the kettle there will be more density in the wort and the gravity will increase (because the water volume will decrease). So at this point, you have higher gravity wort but are below your 5 gallon target. By adding the water to make up for what has evaporated, you are reducing the density of the water and thereby decreasing the gravity. Adding fermentable sugars such as malt extract or even dextrose will raise the gravity again, to hit the target you want. If you find that your efficiency is always a little low, carry a little extra malt extract so when you do batches you can pour some in to raise the gravity.