Dimension not adding up between two sides of a rectangle


I m trying to make some industrial fabrication schematics for my kitchen. I made models for how the different plank components should be cut, but for instance in the component below if you look closely between the left and right side where I design holes ( all holes have diameter of 8mm ) even though the measure tool gives me identical dimensions between the two components and individual distances I end up having 1mm mismatch between the left and right side between the centre of the last hole and the edge of the plank. I can t find a mistake in my model though…

Any ideas ?
Bot-Px-Planks.skp (102.9 KB)

Yep. And this is not a bug. Please edit your post and remove ‘bug’ from the keywords. You have Display Precision set to show dimensions to the nearest millimeter.

But that’s too coarse to show the actual dimensions you set things at.

You also have Length Snapping enabled which can help create issues like this.

Turn off Length Snapping and set display precision high enough so you can see your errors before they become a problem. You can always reduce Display Precision later after you know you made your model correctly.

What version of SketchUp are you actually using? You posted in the SketchUp Pro category but your forum profile says you are using SketchUp Free which is web based.

If you are using SketchUp Free, the Display Precision and Length Snapping are set in this window:


I started with SketchUp Free indeed and set my precision to 1mm thinking it would not allow me to do anything less and avoid such errors indeed!

today I started Sketchup Pro evaluation as I find it pretty useful as a software and I was thinking to eventually buy. So that’s y I posted under Pro category!

Thanks for the valuable info I will try to fix this error :slight_smile:

Precision only affects the display of dimensions. In Pro, the settings are in the Model Info>Units tray. You should also turn off Length Snapping. It is an useless setting that increases inaccuracy instead of preventing it.

Remember that the setting is Display Precision. It has nothing to do with how accurately you model, only how precisely the dimensions are displayed. My preference is to model with the Display Precision set as high as it will go for the units I’m working in. When I later create the dimensioned drawings I set the Display Precision to suit the project and the type of measuring tools that would be used in real life. That lets me catch potential dimension errors before they become a problem.

1 Like

Man I wish it hadn’t taken me 10 years on SketchUp to discover this…only last night. :person_facepalming:

I will always model in the highest display precision from now on.

The fact length snapping is on by default completely mislead me about what it actually does. For whatever reason I just never interrogated it and have always assumed it was necessary and SketchUp is just a buggy and less accurate software. mind blowing.

It might be helpful linking you and future users who arrive here to the discussion in this post’

Length Snapping is great when you are using SketchUp for what it was originally designed for–making quick sketches with roughly accurate dimensions. But SketchUp is most definitely capable of very high precision if the user chooses to model with high precision.

The advice to turn off Length Snapping has been given on this forum for years. I’ve taught all of my students over the last 15 plus years to turn it off and set Display Precision as high as it will go when they create their own SketchUp templates.

Definitely not. This is something I 3D printed from a SketchUp model this morning. It’s a quick model so a little rough but the screws are M6 x 1.0 and the oval plate is threaded to receive the screws. (One screw is holding the clip on the left in place.)

Lousy phone image.

The model.


Your advice is appreciated and I’ll be following it from from here.

I’m self taught (as many others would also be) and when your not aware of what is causing the issue or what you should be searching for on the internet/forum… how do you know?

With hindsight it seems stupid that it’s taken me this long to discover it, but that’s hindsight.

The question is around defaults and descriptions within the software. I didnt adequately understand what length snapping did.
The user base has long evolved from people primarily making rough sketch models. Anyone from architects, jewellery designers to furniture makers or CNC fabricators etc, all want accuracy. Even someone at home modelling a lamp or a car for fun, still needs accuracy for the thing to be at scale and elements to align.

The rare case where you want your cursor to snap to invisible grid of points rather than other elements in the model seems like a bad reason for a default - as others have discussed in the forum above.

Some supplied templates already have Length Snapping turned off. Choosing the right template, and better, making your own template helps to make the modeling process easier.

I have always used my own template but it is a modification of the ‘Architectural Millimeters’ which has a default display precision of 0mm and length snapping on at 1mm. I just upped the decimal value of both but never thought to uncheck length snapping.

I now see the woodwork template has display precision set to 0.0mm and legth snapping unchecked. If only I had started with this template.

Personally I think the default accuracy for the architectural template is too low. While you may never want fraction of a mm dimensions in the final drawing set it is still necessary to have the model accurate. For example divide a length in half that has an odd number or when you array a range of parts small invisible inaccuracy can compound to measurable discrepancies.

Again it’s obvious once you know…

Thanks again.

I’m quite satisfied that my little noob mistake was of value for the general community :stuck_out_tongue_closed_eyes:

1 Like

FWIW: Length snapping doesn’t snap to an invisible grid of points but as you can guess to a certain set length…

1 Like

Correct, which is why drawing a line starting from a point that is for any reason imprecise will yield an end point that is similarly imprecise when length snapping is on. The contamination spreads with each new line you draw.


mmmm. So does length snapping only affect the drawing of lines or also moving of objects from point to point?
For example when I hold shift and move a component to abut another component, I start the move and hold shift until I see the “intersect with face outside of active” at which point I click and complete the operation.

  1. Does length snapping impact this?
  2. Does display accuracy impact how accurately the component is actually placed?
    See I always assumed the placement would be accurate in an absolute sense with Zero gap between the parts regardless of the display accuracy that is tunred on. Intersecting should be just that…intersecting. zero gap.

Length Snapping affects drawing of edges as well as shapes (rectangles, circles, polygons). It also affects the Move tool as well as Push/Pull, Scale, Tape Measure, etc. There’s also Angle Snapping which affects Rotate and the Protractor tool.

You can make it more clear if you set Length Snapping to some large interval and then experiment with the tools.

1 Like

So this was not a test of length snapping behavior, but a test of SketchUp accuracy generally:

  1. I remodeled one of my components (and all its sub components) with the display accuracy set to maximum and length snapping disabled and double checked that all elements were sized exact to .000000 decimal places and placed relative to one another exact to .000000 decimal places. (Checked with tape measure)

  2. I imported this component into a fresh template with the same settings - display accuracy set max, length snapping off.

  3. Drew a rectangular plane on the ground using exact dimensions input by typing 2700,2700

  4. I placed my frame component on the this plane using the mid point of a member as a snaping reference to meet the rectangle’s corner.

  5. I measured the distance from the top of this RHS member to the plane. At one end it is exact: 40.000000mm as expected.

  6. I measure the other end. The dimension reads 40.000005mm

I show the rotation tool placed on the member at both ends to verify that they are both in the red plane.

Is this just hitting up against the limitations of Sketchup’s accuracy? Obviously I don’t need to manufacture to this number of decimal places but more trying to understand the software and how or why those measurements read different at either end.

Thanks again.

Or to better illustrate here is me moving this component around relative to the plane which reveals that when it is placed accurately at one end, the other becomes inaccurate by that small amount. I’ve tested with other parts and this inaccuracy number changes. Some times 0.000003 or 0.000006.

Again I just want a better understanding of the software for better practice moving forward.


I don’t think so. Most likely your component is not accurate in the first place.
Please share the file you are working with.
Otherwise it will be hard to explain where things go wrong on your side.

Accuracy Test.skp (529.1 KB)

Ok. Good to know.

I’m guessing because the components were originally modelled with the display accuracy lower and length snapping on, there must be some inaccuracy still in there even after rebuilding.

Could having ‘angle snapping’ checked do this?

Thanks for taking the time to have a look.