Quick Tank Size Question Dimensions

[buzzfrog]

so i was at petco looking at there tanks today, there 75 looks bigger and there messurements are all a 1/4 more thank mine, but i put it into this sites tank calculator and it says 75, i also tried 2 more online tanks calcs and they all say 75, so i am confused, mine is Lx 48 H-18 W-20 as said petcos tanks all say L-48 1/4 H-18 1/4 W- 20 1/4... so yea... your opnion, sorry if this is dumb

 

[Ps3Steveo]

Glass thickness maybe?

 

[buzzfrog]

Wow, man thanks, I feel dumb that I didn't think of that