The solution to just right amount of sides to put on a circle

I realize a lot of my student tend to just put inn a random number to get a clean circle with more the 24 sides. But there is actually a set of perfect numbers. Time to Math nerd!

First off anything the size of a screws or other details should always stay low poly for large drawings. the choice here are 8, 12 or 16.

For larger circles that need more sides like for a CNC cut or 3D print the options are
24, 48, 72, 120 or 144.

The perfect number in my opinion for large circular flats is 120.

Why you ask?

Well the numbers 24, 48, 72, 120 and 144 are all numbers that will
devide by: 2, 3, 4 ,6 and 8. Or if you like pizza slices in 180, 120, 90, 60 and 45 degrees.

Additionally 120 also divides by 5.

Feel free to put these values in a dropdown selector in entity info for circles Trimble! :wink:


That logic makes sense, I tend to use 48 and 96 often for similar reasons. I do use 120 and 360 mainly for 3D printing, but the facet count in those cases is dependent on the dimensions of the part as the real goal is to keep the facets below the printer resolution.

For CNC work, outputting toolpaths for routers, lasers or plasma cutters I use the fewest number of sides practical and then output true curves in 2D via .dwg or .dfx.

Of course, the β€œbest” number of facets is also dependent on the SketchUp model dimensions to carefully avoid the low end resolution tiny face limitations.


I use a plugin to calculate the number of sides more efficiently. Making it evenly divisible by four preserves the ordinal points of the circle.


jrh_n_calc.rbz (814 Bytes)


Do either of these counts give a smooth to the feel circle, or are you using them for another reason?

A smooth to the feel circle is certainly the goal and either of these counts can yield that but the third crucial piece of information is circle diameter. 120 facets on a 5” circle (127mm) will still show the facets in a print, however with the same count on a .25” (6mm) circle the individual facets are well below the lowest resolution of most FDM filament printers so the part will appear smooth. So, yes, by using a high facet count relative to the circle diameter (SketchUp accepts up to 999 side for a circle) one can print relatively smooth sided objects. The reasons for using 120 and 360 and not 247 or 334 are for ease of use and divisibly as outlined in the first post.

Wow. Life Pro Tip. Thanks for linking to the extension! I found that 16 for a 1" radius looks kind of rough, but since it gave me 16, I just doubled it to 32 and liked that, AND knew it would divide by 4. Nice.

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Good point!
Little point of interest: any circle has (and keeps its) either two or four cardinal points.

Number of segments in a circle:

  • uneven β€”> 2 cardinal points i.e. one endpoint and one midpoint across
  • even and divisible by 4 β€”> 4 cardinal endpoints i.e. two endpoints on (or near) one axis, the other two endpoints on (or near) the other axis.
  • even but not divisible by 4 β€”> 4 cardinal points i.e. two endpoints on (or near) one axis, the other two being midpoints on (or near) the other axis.

(I hope I didn’t lose count)

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Thanks for explaining that