If it's the "oil" drain plug, the size wrench is, better yet use a socket wrench=13mm.
The wrench size is 14mm.
What wrench size is need for a 2007 Honda Civic oil plug?
It takes a 17mm Allen wrench to remove the fill plug.
15mm
13mm
The wrench size should be 15mm.
Mine is 12mm wrench, but some are different.
It should 14 mm wrench.
If the drain plug is original equipment, it takes a 17mm wrench or socket.
If it is an original style drain plug a 15mm wrench is what you want.
The original engine oil drain plug wrench size should be 15mm.