Millimeter discrepancies in SketchUp

Hi all. I just tried SketchUp today and got a little confused with measurement discrepancy with the measure tape. Is it normal to see measurement discrepancy as much as 1.1 cm in SketchUp?
My experience was this: I drew a smaller rectangle inside a larger rectangle (say the length of the larger rectangle is 2500 cm). Both rectangles have exactly the same offset width. But when I added the total interior lengths and the offset widths, the result wasn’t exactly 2500. It was off by 1.1cm. What could I possibly miss?

Upload the file so someone could check!

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SE Home SketchUp.skp (659.6 KB)
Here’s the file I was working on. I was checking the length of the larger rectangle (right side), which should be 2267cm. But adding all the interior lengths and the offset (15 cm) resulted in 2265.9.I know it’s only 1.1cm difference. But I’d like to understand why.

If you are concerned about avoiding those sorts of discrepancies, you should increase precision and turn off Length Snapping.

You also have a lot of reversed faces. It’s best to stay on top of them and correct them as you go.

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Rectangle definition:
a plane figure with four straight sides and four right angles, especially one with unequal adjacent sides, in contrast to a square.
You have 2 right angles at one end, the other end has an 86 degree angle and a 94 degree angle.


Oh sorry, I was wrong with the term. Not very good English.
But I’m aware of the different angles on the back.
2267 was the exterior length of the right side of the larger plane. I made sure I checked all the interior lengths on that same line: offset 15 + 591.1 + 1330 + 314.8 + offset 15 = 2265.9.

No worries

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And has been said many times here, only groups or components should be assigned a layer.
All edges and faces should be on layer 0



I’m sorry but I’m not sure I understand. The discrepancy is 1.1cm, while length snapping was set at 0.1cm only. Do reverse faces affect the measurement that much?

Also, I didn’t know about and wasn’t aware of making reverse faces. Any suggestion how to avoid making them?

Oh I see. I’m learning. Thank you for reminding, Shep.

Also note the lengths on the end with the odd angles is reported as approximately 802 and 771. Pay attention to the tilde in front of the number. The approximation will account for the difference.

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Offset may be 150mm (15.0cm) but at the corner less than 90 degrees the offset measured along the large edge direction is ~161mm, that’s nature.

- (also explained by @slbaumgartner in next post with an excellent image)

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It is indeed because the corner is not square so the dimension line from the interior corner does not pass through the outer corner:


@slbaumgartner, @RLGL, @g.h.hubers
Wow guys. Thank you for cracking the mystery for me.