About how many pounds does one cubic foot of granite weigh?

166.5 lbs on average per cubic foot.

http://wiki.answers.com/Q/How_much_does_a_cubic_foot_of_granite_weigh

This site says 168 lbs though.

https://www.aqua-calc.com/calculate/volume-to-weight/substance/granite-coma-and-blank-solid

Granite weighs Approximately 168 lb / cu ft

The density of granite is approximately 2.7 g / cm3.

https://en.wikipedia.org/wiki/Granite

1 g = 0.002204623 lb, so 2.7 g = 0.005952482 lb.

http://www.convert-me.com/en/convert/units/weight/weight.gram.en.html

1 cubic centimeter = 0.000 035 314 666 721 cubic foot

http://www.onlineconversion.com/volume.htm

Combining these figures, 2.7 g / cm3 is equal to 168.6 lb / cu ft.

The density of granite is not a specific figure, however - different samples have different densities because the mixture of constituent minerals is not in a precise ratio. I use the figure of 2.7, but the link above about granite says that values can very between 2.65 and 2.75. This gives a range of potential values between 165.4 and 171.7.