Gravel and crushed rock is typically 2100 lbs/yd3. A 4 yd3 load is about 3.0 to 5.6 tons (typical 4.2 tons). Gravel and rock are dense enough that haul limits usually dominate. Plan around controlled fill and swap logistics.
Gravel and crushed rock is usually a weight-first decision surface. Treat volume as secondary after tonnage limits.