Getting the size/Distance of the detected wall using ARCore, How?

I want to get the size of the detected wall or any surface, get the dimensions in meters without placing any game object over detected plane. Please help

 

I am trying to do this myself. I have seen an APP which is pretty accurate measuring with the camera so it can be done. First try getting the distance to the detected plane. I'd place a small actual ruler on the surface and then a GameObject by it to compare the size. Get the "actual" size of the GameObject by having a box collider on it and know what that size is, and assume Unity uses meters. Also realize that ARCore doesn't detect the whole wall, just a polygon portion, and you can also check the bounds of the polygon but then you're just going by Unity units and I know you want the actual in meters.