If the tailpiece will not line up with the trap move the trap into its original position tighten the collar with the pipe wrench and obtain a flexible tailpiece extension for your drain.
Bathroom sink tailpiece too long.
There is lots of play so no worries.
If it s too short add a tailpiece extension which is a short length of pvc pipe.
Trim the tailpiece to fit.
You doing this for measuring purposes only.
This bathroom sink tailpiece too long graphic has 20 dominated colors which include uniform grey silver tin cab sav steel pig iron sunny pavement thamar black kettleman snowflake black white benthic black driftwood bengala red honeydew rusty nail foundation white himalayan salt ivory.
A pipe cutter would be a bit more suitable than a hacksaw but if you only have a hacksaw just clean up well with a file after sawing.
Cut the extension to the proper length.
Then cut tail piece accordingly.
I suggest that you do dry run meaning assemble and hand tighten all drain pieces including tail piece first.
If it s too long cut it with a hacksaw.