It's never a good idea to guess with measurements, that's what measuring tools are for. No need to look for a power outlet, since it runs on batteries. Just get at it!
From ManoMano
Stabila - 18574 fls 90 Floor Line Laser STBFLS90
Conrad Electronic
Stabila FLS 90, 3-pcs Tiling laser Range (max.): 15 m
This product is also available at 2 unverified merchants.