OG way Low

I just brewed an IPA and my target OG was 1.071 and I ended up with only 1.054. My efficiency into boiler was pretty good (my target was 1.043 and I got 1.046), 70% efficiency.

My volume into the fermenter was over by .25 gallons--not nearly enough to account for the large gap in OG. Does anyone have any thoughts as to why I'm so far off?

Check your boil off percentage,  I have to set it at 30%/hour to get an SG of 1.049 and 7.44 gallons into the boil>

Fred

Shouldn't I be setting my boil off percentage so it's equal to the volume I'm losing during the boil? I lose about 1.5 gallons on a 5 gallon batch...so I have my boil off percentage set to 18% which corresponds to 1.5 gallons per hour...doesn't that make sense?

Makes sense given accurate measurements, but. . .

Given you pre-boil gravity and you final gravity, you did not boil off enough to hit your FG.  It could be that your pre boil volume was low but your final volume was high.

best guess is inaccurate measurements,  the most common cause of "poor efficiency", "low FG", etc. 30% loss per hour is typically too high.  The other option is your preboil volume should be higher and perhaps your boil off rate is off too.

Fred