The best replacement for arc length is chord length.

The best alternatives to arc length are rated as following:
★★★★★  chord length
★★★  arc measure
★  chord
★  line integral
  central angle
  cord length
  circle formula

Your alternative for arc length is not listed? Suggest!
Speaking about arc length, one probably shouldn't forget about radius.

Other search terms related to arc length and their ratings are:
★★★★★ radius
★★★★ central angle
★★ radius and central angle
★ chord and radius
★ circumference
You have in mind a companion for arc length and it is not yet here? Propose!



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arc length
chord length
arc measure