Paper collections should be measured via the direction of paper being filed. Generally, that is the width or length of a box, but things can get tricky, especially with a flat box. When in doubt, ask the Special Collections Librarian! In general:
2.5" doc box = 0.21 Linear feet (LF)
5" doc box = 0.42 LF
7" doc box = 0.58 LF
Records carton (letter size) = 1.25 LF
Records carton (legal size) = 1 LF
3" high flat box = 0.25 LF
Quick Tip: To measure linear feet, measure the length in inches, then divide by 12 to determine linear feet.