How to calculate angles in complex constructions?


Hello fellow sketchup users,

I’m fairly new to the program and still figuring out some of the basics. But I’m getting the hang of it pretty quickly. I’ve just run into a little issue…

A friend asked me to design a climbing wall for his backyard and so I did. To be able to build it I have to saw my plywood into the right angles. I just can’t seem to figure out how to calculate the mitre angles of all the areas where the boards meet.

Can anyone help me out? Is there and easy plugin for this?

Thanks in advance!



The simplest way may be to use the protractor tool with its “drag along edge” feature to measure the angle between the two planes to be mitered. The miter angle is half the angle between the two planes,measured perpendicular to the edge between the planes. The attached animation shows this idea for two rectangles that I have intentionally rotated out of alignment with the axes so you can see how the “drag along edge” feature works. In the measurements box you can see that the angle between these two planes is 150 degrees, so the miter angle will be 75 degrees.


Some interesting miter cuts there for sure!

I have a plugin/extension called “angular dimension” which allows you to dimension angles within Sketchup similar to the native “linear” dimension tool.

Its available from the Extension warehouse I believe.(free).

I myself find it really useful, however @slbaumgartner suggestion works fine too, take note of the miter angle being only half of the measured angle.


Thanks for the plug! As the author of that extension (and also co-author with John McClenahan) of its successor Angular Dimension 2, I thought about using it to mark the angle. The reason I didn’t is that I think the OP was asking about the edge miters between the boards, not the angles at the corners of the boards. To find the miters, you need to measure perpendicular to the edge between two faces. To do so using Angular Dimension you must first construct two lines perpendicular to the edge because the extension is happy to measure angles between any two 3D lines, it knows nothing about “perpendicular” or “in face”. In my simple rectangle illustration the adjacent edges are perpendicular, but in the OP’s image they clearly are not! So, I chose the faster method using the native protractor tool. The main downside of that way is you have to note the value as you see it in the measurements box, there is no persisting annotation for later.


For complex timber assemblies I use Clark Bremer’s Plugin ‘Angle Between Faces’ -

You select the line between 2 faces and right click, your angle is shown in the context menu.


Yes, thinking about it I see what you mean, although “angular dimension” would get the angles for the outside edges, not so well for the miter.
It was the “persistent” annotation I thought of. It got annoying trying to remember angles using the protractor too, that’s how I came about the plugin.

Looks like @bmike has a suggestion worth investigating for this too, may fit the job perfectly. I haven’t come across that one before.


Even faster than the protractor technique, but it also doesn’t generate any lasting annotation.


Oh the pros and cons!
Maybe there’s an idea for someone to work on then?


Thanks everyone for your answers. The protractor tool works great for this. As @slbaumgartner was saying I’m looking for the miter between the boards. And the protractor works fine for this.

I’ll look into the suggested plugin that @bmike suggested.

Thanks again!


For the plugin I suggested you need to divide by 2 for the miter, as it gives you the angle between faces.

Be careful with the protractor - that is the way I used to do it, and if you aren’t careful to be perpendicular to the line, you end up with results that can be off.

What I do, when I have a complex roof that needs parts detailed - is I use the plugin and take a screen shot of the dialog on the right click, showing model context (not that different from the images I posted). I then go back and add notes to the drawing - putting in the values of the angles from the screen shot on the appropriate locations.


That’s where the drag-along-edge technique comes into play. It assures the protractor is working perpendicular to the edge regardless of how the edge is oriented.


Yes, a good technique.

I do a lot of teaching / coaching - and I can assure you that folks are really clumsy with the mouse / movements / etc. - it takes a lot of practice for people to be comfortable and accurate… that is all my suggestion meant.

And, on the miter angle, yes, it depends on how the saw is oriented to the workpiece. In my world the craftsmen usually bring the saw to the timber, so setting the angles depends on left / right tilt, and which side of the piece they are cutting from! Miter angle does not always = saw angle - the real world always complicates things!



You remind me of how my wife (who is mildly dyslexic) struggled to learn how to use a mouse at all. She determinedly moved the mouse to the left and expected the screen cursor to move to the right! The coordination just wouldn’t “click”.