Height of mesh (like a bridge)

Hi, I wanted to understand how to calculate the existing height under a gameobject which could be a bridge, just to understand if the player can pass under or not. I don't want to use the navmesh, just know the space between the ground and the underside of the bridge.
With raycasts I can know at what height the bridge is, but this does not imply how much space (based on its thickness) it occupies under itself.
I hope I have expressed myself well and that google has translated clearly.
Thank you all for any advice you can give me

bridge > /////////////////////////
bridge > /////////////////////////////
bridge > /////////////////////////////////
bridge > ///// traversable height
terrain > _______________________________