The following conversion factors for base course and blacktop paving where given to me by a paving contractor as the ones he used for estimating:
Material Compacted Tons/SY Tons/CY
Thickness
Stone Base 6" 0.33 1.98
8" 0.44
10" 0.58
12" 0.66
Blacktop 1" .055 2.25
2" .110
3" .165
4" .220
However, you can compute any of these yourself using the unit weight of the material, which can be found in any engineering ref. book or AISC manual:
tons/cy = [(lbs/cf)x(27 cf/cy)]/2000 lbs/ton
Hope this helps!