Copper Ptrap snapped during bathroom demo, how to fix?
Soak it good with penetrating oil. Then use a pipe wrench if you have one. Righty tighty, lefty loosy. Yes your measurement will work. Most kitchens are 1 1/4" and bathrooms are 1 1/2" however this can be different. Looks like you have 1 1/2". Get a new kit similar to this http://www.homedepot.com/p/Everbilt-1-1-2-in-Plastic-P-Trap-C9704B/205153793 plus any adapters you need that are not in the kit. Some kits have everything you need and more, some only a few necessary parts.