From The Collaborative International Dictionary of English v.0.48 :
Lengthiness \Length"i*ness\, n.
The state or quality of being lengthy; prolixity.
[1913 Webster] Lengthways
From WordNet (r) 3.0 (2006) :
lengthiness
n 1: amount or degree or range to which something extends; "the
wire has an extension of 50 feet" [syn: extension,
lengthiness, prolongation]
2: the consequence of being lengthened in duration [syn:
lengthiness, prolongation, continuation, protraction]