Marklin 24188 straight track piece is 188.3 mm / 7-13/32" long. This with the 24172 are your standard straight track pieces.

Remember to use the 24188 with the 24172 straight track. When you lay a long stretch of straight track, use 24188 - 24172 - 24188 - 24172 and so on. You do this to maintain the correct geometry of your layout. Turnouts and their curved portion have the same lengths as the 24188 and the 24172.

Also sold in box of 10 under item 24188-1