Last updated July 28, 2026
ARCDIST measures the length of part of an arc without cutting the arc up to do it. You show it two points along the curve, tell it which arc they sit on, and it works out the arc length between them.
The alternative, before this, was to break the arc at both points, use LIST or DIST on the piece you wanted, and then undo the breaks — which works but leaves you nervous about whether the drawing really did go back the way it was. That is what the listing means by “without breaking the lines”.
It is one of ours: written by YZ under YZ Enterprise, dated 12 November 1997.
The geometry it uses
Worth setting out, because it explains why the routine asks for what it asks for — and it is a neat piece of school trigonometry doing real work.
Two things fix an arc length: the radius of the arc, and the angle it subtends at the centre. The radius is easy — it is stored on the arc, so selecting the arc hands it over. The angle is the harder part, and that is what the two points are for.
The straight-line distance between your two points is the chord. Drop a line from the centre of the arc to the middle of that chord and you have a right-angled triangle: the radius is the hypotenuse, half the chord is one side, and the angle at the centre is half the angle you are after. From there it is Pythagoras and an inverse trig function to get the included angle, and then the arc length is that fraction of the full circumference.
So the two prompts are not arbitrary. The first gives the chord, the second gives the radius, and between them they pin down the answer.
Two things to be careful about
Snap to the arc. The chord is measured between the two points you pick, and the maths assumes both of them are genuinely on the curve. Pick approximately and you get an approximate answer, with no warning that anything is wrong. Use a nearest or endpoint snap.
It measures the minor arc. A chord cuts a circle into two arcs, a short way round and a long way round, and the calculation returns the short one. If what you want is the long way round, subtract the answer from the full circumference.
The arc selection uses the nested form of picking, so it will read an arc inside a block rather than refusing it — useful when the curve you are measuring is part of a symbol.
Command reference
The file defines a single command, ARCDIST, and reminds you of it when it loads with “Type Arcdist to begin……”.
How to load it
Unzip ARCDIST.zip and load ARCDIST.LSP with APPLOAD, or add it to the Startup Suite. No support files. Our AutoLISP guide covers loading.
Step-by-step usage
- Turn on a suitable object snap — nearest or endpoint.
- Type ARCDIST.
- At “Pick two points on arc:” pick the start and end of the portion you want measured.
- At “Select arc:” click the arc itself.
- The arc length is reported at the command line.
Sanity-check it the first time by measuring a full half circle, where the answer should come to the radius times pi.
Compatibility notes
The listing records it as working on AutoCAD R14 and 2006, which spans a decade of releases. It does arithmetic and reads one property off an object — there is very little in it that could break.
Plain AutoLISP with no dialog boxes and no Express Tools calls, so nothing requires the full product; LT users on LT 2024 or later, the release that brought AutoLISP to LT, should be able to run it. See what runs on AutoCAD LT. It measures and reports without touching the drawing, so it is one of the safest things here to try.
Download
| Name: | ARCDIST |
| Description: | Finds the lenght of part of an arc without breaking the lines! |
| Type: | AutoCAD AutoLISP Routine |
| Author: | YZ |
| File Size: | 1 Kb |
| Cost: | Free |
| Worked on: | AutoCAD R14, 2006 |
| Download File: | ARCDIST.zip |
Related routines
- ADDLENGTH — totals the length of whole lines and arcs.
- HowFar — straight-line distance with a dialog readout.
- PDIST — running distances along a polyline.