Three Feet Versus Seven Feet

The difference between a 3 foot dig and a 7 foot dig is exponential, not linear.

The first dig is maybe 3 cubic feet of dirt if you can pop in with a single hole.

The second dig requires a hole big enough to stand in while shoveling dirt up and out. Figure 5 feet on a side, or 175 cubic feet of dirt, or about 6.5 cubic yards of dirt.  It’s a lot.