Calculating Bittering Units for your homebrew?

Is there an easy way to calculate the bittering unit when dumping your hops into your wort?  I have tried to find some easy calculation, but it doesn’t seem to make a whole lot of sense.  I have been using hop pellets.

For example:  I recently brewed a an IPA from a kit which called for 1 oz Pilgrim Hop Pellets, 11 alpha (full boil) and 1 oz First Gold Hop Pellets 7.3 alpha, during the final minute.  I added an additional 2 oz of Cascade Hop pellets at approximately 1/4 oz every 7 minutes.

Based on that can someone attempt to tell me the bittering units and how they came up with that calculation?  I started brewing about 10 years ago, but took an 8 year hiatus and this was my second batch since returning.

Many Thanks!

This should help:

http://www.howtobrew.com/section1/chapter5-5.html

There are about a half-dozen utilization correlations in common use, and there can be some pretty extreme variations between them. The best thing to do is settle on one and use only it, so that at least you’ll be able to compare numbers between recipes.

I like Glenn Tinseth’s: Hop Utilization Page

That’s also the curve that Palmer uses in the link tygo posted.

So you can’t fully determine what your IBU’s are until you take your OG reading?  You can target the IBU’s based on your target OG, correct?

It’s worse, you pretty much can’t count on determining your actual IBU levels period.

The physical reality of the number of factors that affect your IBU level is daunting and no one model captures it all.

If you want to predict IBUs, then choose a formula and gain by experience a knowledge of what “60 IBUs Tinseth” means tastewise. And yeah, you’ll need to have the gravity to get to cracking the numbers. It’s actually a good idea to get the gravity before adding the frist hops so you can adjust hopping levels according to your actual gravity (should you miss for some reason)

If you want a ball park way of quickly doing hops, you could always just ball park things via HBUs (e.g. weight of hops * AA%) and know from your experience what that means in your standard gravity beers.

I do: ounces x alpha , then multiply by 3.75.

This is just for the bittering addition, and assumes a 60minute boil of an average strength wort of around 1.050, and 5gal final volume.

Here you go… start here.  http://www.tastybrew.com/calculators/