One cubic yard of Ca6 approximately weighs 1.8 tons (3600 lbs.).
Ca6, also known as road gravel or grade 8, is combination of 3/4″ limestone and limestone fines that is most commonly used to provide a base for paver patios, sidewalks and driveways. It is sold in bulk by the weight.
The formula below will help calculate an approximate quantity in tons.
Length (in feet) x Width (in feet) / 12 x Depth (in inches) / 18 = Tons
You can use this Bulk Material Calculator provided by Keller Material, Ltd.