How to calculate distance from ground

I am making a game with a teleportation mechanic like ender pearls in Minecraft. Here is the code for the teleportation -

  private void Update()
     {
         if (shouldTel == true)
         {
 
             transform.position = new Vector2(telPoint.transform.position.x, telPoint.transform.position.y + 1);
             
             shouldTel = false;
         }
     }

I am using a tilemap for my level design (my game is a 2D platformer). So now what happens is that if I throw a crystal on the ground, I teleport a bit high in the sky because of the offset of 1. And if I throw it at the side of an in-world block (About, 24 PPU) I teleport on top or at the side of the block. But if I throw it at the side of a wall more than 3 blocks high, I teleport inside the wall. Is there any easy way to calculate the distance to the top of the tilemap collider and store it in an int variable?