safety distance to wall

Depends. The stopping distances are for protecting humans from the automation, not protecting the automation from damaging itself. So a solid wall that the robot can't punch through (and maybe hit someone on the far side) could be treated as not needing a stopping distance. For example, a major automaker recently changed their stopping distance for small robots inside plexiglass enclosures to basically zero, b/c the robots can't really punch through the plexiglass easily.

"Stopping distance" values are generally generalizations, as stopping distance varies depending on robot speed, payload, and pose. 12-18 inches (300-1450mm) is pretty typical, but since those are Safety-related, they're fairly conservative. Then there's the extra factors of Safety-rated speed limitations, which can be used to reduce those stopping distances.

Those general rules are usually used b/c doing individual testing on every robot in every condition simply isn't practical. If you really need to find your absolute minimum stopping distance vs this solid wall, you could test the robot with the worst-case working payload, and determine your stopping distance for that robot in particular.

the point is that safety distances and guarding are there for just one reason - protect humans.

they are not there to protect objects.

You can have robot crash into wall or get inside the press and turned into pancake by the press and nobody cares. sure it is inconvenient and expensive but that is just material cost and - that is replaceable, all you need is money, there is no police investigation and nobody goes to jail. and if you have money to waste you can keep crashing robots all day long. nobody will complain or bother to notify authorities.

but if you have someone killed, that person is gone and no amount of money will bring that person back to life - at least not in exact shape, form and mental state. maybe you can create a clone but that will still not be the same person with same memories. so yeah, in that case all kind of activities will be triggered (police investigation etc...)

now that the first thing is explained, lets be clear - there are places where distances to solid surfaces matter (wall, column etc.). but again - ONLY in respect to protecting HUMANS. robotic safety standard states what velocities and distances are required to not harm humans when they need to be inside the cell, for example when teaching points.

for that you can use soft limits or workspaces. and if your robot supports range limits that is a possibility too. basically those options would be the first line of defense.

using other sensing means is possible too. if you have laser scanner, many will support more than one field so one can reduce speed if specific zone is entered. this can eliminate or drastically reduce magnitude of the impact.

also use correct load data and collision detection.

also (depending on what part of the robot may be colliding) you can also add breakaway clutch. this way if the hard tool is driven into hard surface, clutch disengages and stops the robot. different variants exist (using pneumatics, spring, magnet)

Why?

You have the robot.

Use it. Let it do the measurement...