How can i set a specific length for an edge? I want to build a room with specific length. For example 40cm. So, i want to put a specific value somewhere. Answer only for Blender 2.8/ 2.81 pls. BTW sorry for my bad english
Just to illustrate Ray's comment.

Enable ✓ the Mesh Tools addon.
Preferences > Addons > Edit Mesh Tools


Switch to Edit mode, to see the Mesh Tools addon.
It's under Sidebar > Edit > Mesh Tools