Standard Conversion Grain to OG?

Is there a good web app, or perhaps a ball park conversion formula for lbs. of grain to OG assuming 70% efficiency?

I'd like to be able to look at a grain bill and modify it slightly if I want it to be slightly stronger or weaker, but do it in a mathematical way.

Additionally, I would like to be able to measure my OG and see how it compares to what it should be. A recipe giving you what they got is all well and good, but I would like to be able to check my own version of a recipe against a specific value especially if I tweak the grain bill a little bit.

Thanks in advance.

Well, 70% efficiency means that you got 70% of the max potential extract out of a particular weight of grain. American 2-row is usually 36 or 37 pppg (theoretical max of 36-37 gravity points for 1lb of grain in 1 gallon of water). So, in that case 70% efficiency would mean .7*36.5 = 25.55 points per pound per gallon.

Try the free online calculator Beer Calculus at hopville.com. Very handy for formulating recipes. It has a large selection of grains, will calculate IBUs from hops and has style guidelines for recipe formulation.

Beersmith has many more features and is more customizeable, and is only $20 one time.

I see beersmith referenced all the time so i think ill end up going that route. Thank you for the info, i found i was around 50% on my first batch, so i will focus on upping that next batch.