Obviously not familiar with caliber designations.
A "caliber" is an archaic unit of measure for designating the diameter of holes, where 1/100th of an inch is 1 "caliber".
.01" = 1 caliber
.224" = 22 caliber
.257" = 25 caliber
.308" = 30 caliber
.500" = 50 caliber
et cetera, ad infinitum.
So a truck 50" wide would be roughly 5000 caliber, if you chose to use the measurement of the cab width.
__________________
I disagree, unless you refer to your weapons as "point" 50 caliber.
http://www.thefreedictionary.com/caliber "The diameter of the bore of a firearm, usually shown in hundredths or thousandths of an inch and expressed in writing or print in terms of a decimal fraction: .45 caliber.
c. The diameter of a large projectile, such as an artillery shell, measured in millimeters or in inches."
also, a U.S. Army training manual from the Army Marksmanship Unit which refers to "caliber .22," "caliber .38," and "caliber .45" on page 11, and again on pages 12, 14, 27, 93, and 94. Pages 93 and 94 also refer to a no decimal "22 caliber long rifle" and a no decimal "22 short," respectively, so it appears they are interchangeable in writing.
http://www.saveourguns.com/Ar_Marks_Un_Pistol_Train_Guide.pdf
if the truck were 50" corner to diagonal corner, it would be 50.0 caliber, as opposed to .50 caliber. and, as it's 50" wide and 76" tall, the caliber will be different. if you made a circle touching two corners the circle's diameter would be 93 inches and some change, hence 93.413 caliber.