You could measure the range of the workbench, then put up a grid. You'll have to anyway to keep the base repaired.

Or maybe the core wood beams? At least the bigger ones are 4m instead of 2m

Honestly, I'd use the Ruler mod.

I use core wood beams. For you, that'd be 23x20 beams. Tip: put a marker (I use 1m vertical square beams) every 2 or 4 core wood beams, so I can measure everything without having so much wood tied up.

looks like the radius of a workbench is 20m. thanks for the tips y'all

A soldier in the United States Army, when marching, uses a 30-inch step. That is roughly equivalent to three quarters of a meter.

I have seen many captains, majors, first sergeants, and sergeants major pace off the dimensions of a field when allocating space for a company or battalion to camp.

A viking may use a similar strategy. I have laid two two-meter horizontal beams on the ground end to end and then counted the number of seconds it takes me to traverse that four meters at a walk (toggled with the C key). For a square or rectangular area, it is then easy to place a corner post and then pace off the desired length and width.

The margin of error seems to be two or three meters but once one knows the number of seconds walking four meters takes, one cam dispense with laying out beams. One needs only corner posts.