I have always ripped fabric and then cut off the frayed threads. I began sewing 50+ years ago making clothing and drapery. My grandmother cautioned about finding the straight of grain. Have always wondered why quilters never bother with this very important step.
Further, ripping always give a much truer length. Most places add an extra inch for the pulled threads. Try this. Rip across a piece of fabric on both ends; then measure what you have. Bet it's less than you paid for.