Trying to learn more about Precision and snapping

I am slowly learning SketchUp within the context of designing hobby wood working projects, and finally getting to the point where I am taking dimensions seriously.

I have been having trouble understanding how precision and snapping works in SketchUp.

I think I understand the basic premise of these concepts, but I have created some confusing situations.

For example, I have tried setting snapping to larger increments such as 1/8" with the intent that every shape I make is dimensioned in 1/8" increments.

The dimension labels will display the 1/8" increments but it seems like the shapes are often times not exactly formed in the 1/8" increments. It seems as if the dimension labels include a rounding error.

I imagine I am missing a basic concept, and tried searching for info, but haven’t gleaned any insights.

So, what should I do if I want to maintain very fine precision but enjoy the convenience of working in the increments that are common in wood working?

Thank you!

Simple answer, turn off length snapping as it is basically useless and can produce errors.

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Most users, me included, find that turning off Length Snapping makes it much easier to work with Precision. Enter specific dimensions as you are modeling if those dimensions are important to you. When I am working in Fractional units I prefer to set Precision as high as it will go (1/64 in.) This doesn’t make the model any more precise but it makes it possible to see small dimension errors if they occur.

Turn off length and angle snapping for the reasons you mentioned. Set the drawing precision to the smallest unit for the system you are using. eg 1/64 for the imperial system. When you build the project you can use any tolerance. Build to the nearest foot if you wish.

The reason length snapping can be an issue is if you set it to a specific length, then try to draw an edge to very close to that length but it isn’t exactly where the nearest endpoint that you should snap to is, it can either snap short or long by a small amount that is really hard to notice.
These tiny errors can multiply through a model and you can end up with apparently flat walls that are covered with a spiderweb of geometry because everything is ever so slightly out of alignment.

These errors are so small that they are hard to actually do deliberately.

Using the standard snapping to the inference points is a far better option.


A fundamental point the others didn’t mention is that the precision setting in SketchUp affects only the display of values, it does not cause rounding or truncation to that unit when you create things in the model. If you set 1/8" as the units precision, you can still draw things that are, for example, 11 55/64". The display will show that as ~11 7/8".

Length snapping causes newly drawn lengths to snap to your specified value, but precise placement and alignment still depend on where you started and how you draw.

There are two ways to assure precise measurements in SketchUp, neither of which involves length snap:

  • Type input measurements while drawing
  • Snap to existing geometry that is known to be accurately placed and sized.

Thank you to everyone!

The info is very helpful.

Thank you!

See this topic…

The increments one considers ‘common in wood working’ depends upon where one works wood.
Few professionals in the millwork industry find joy in working with fractional inch increments.
AWI Standards have been expressed tolerances in decimal inches for years.