the specific gravity of calcite is 2.71. If there were no voids in the broken rock the unit density of limestone would then be 169 pcf. If there are 30 percent voids (guess for broken rock), the dry density would then be 118 pcf. So, 120 is a resonable value.
since we don't know the specific gravity of your limestone and we don't know if it is crushed or screened or just rough blasted material from a pit, then we really have no idea what either the unit weight or the void ratio is. so bulk density and volume of a stockpile could vary immensely.
for example, specific gravity varies from 2.3 - 2.7 according to one source I checked and void ratio could be anywhere from 20% to 40%; resulting in bulk density varying between between 86 to 135 pcf
The specific gravity of the limerock (limestone) in my area is around 2.45. Compacted unit weight of limerock runs from about 118 to 130 pcf. Loose, it will be somewhere between 105 and 120, depending on gradation.
Do what OG said...easy, cheap and reasonably accurate.
Thank you for all your answers! It has been really helpful. The aggregate being delivered is 75 mm minus and so I estimated the density to be around 120 pcf.