That doesn't sound right. AHB sends their LME in 1 gallon buckets. I have had 9.5 lbs sent in just one bucket. there was a little headspace left so I'd say it's closer to 10 lbs per gallon.
I'd say that's a safe bet but if I were you I'd try to get more accurate measurements. Fill up a gallon bucket and weigh it. If you don't have a scale, go to your local grocery store, go to the produce section and then use their scales.