Drawing Accurately in SketchUp

There is a misconception among some people that SketchUp isn’t “accurate enough” for their needs. That is a completely inaccurate statement, and it drives me crazy. In this article, I’m going to debunk this myth, by showing you many ways to draw with precision and accuracy in SketchUp.

Ok, I can understand why people think SketchUp can’t be accurate. In my experience, I’ve found it revolves around two things:

1. SketchUp isn’t parametric. If you draw a rectangle, or a cube, you can’t go find the cube “properties” and change the length, or height, or whatever. SketchUp just doesn’t work that way. And thank goodness for that.
2. The VCB (value control box) is that mystical little box at the bottom right of your screen that you see numbers fly in and out of, but you can’t figure out how to click on it in order to feed it dimensions. The VCB is very helpful, you just need to understand how it works a little better.

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Your Opportunity for Accuracy

Whenever you use any drawing or modification tool, SketchUp gives you the opportunity to declare an absolute dimension immediately after (or during) the use of that tool. Each tool has a different set of measurements it can accept, but they are pretty easy to figure out.

For instance, if you draw a line, you can declare the length of that line, simply by typing in a dimension on your keyboard, and pressing enter. You can type in a dimension in any unit of measurement you wish. You’ll notice, when you type in the dimension, it will appear in the VCB. All of these random dimensions below are acceptable input for declaring measurements when requested, and all equal 1 meter (If my math is correct) :

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As you can see, SketchUp is pretty easy going when it comes to unit of measurement. Feet and inches can be input as fractional or decimal, you can also input feet AND inches at the same time. Just separate then with a space.

If you don’t specify a unit (by just typing a number), it will assume you’re want to use the model default units, which you can change in Window -> Model Info -> Units.

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Clik here to view.The rectangle tool is a little different. If you were to draw a rectangle, there are two dimensions you can input: the length, and the width. You can type in both the length and width, separated by a comma, or you can choose to only declare one of those, leaving the other as is. If you wanted to change the length, you’d type 4′ ENTER. If you wanted to change only the width, you’d type ,5′ ENTER. (Notice the comma before the dimension.) This is handy when you are snapping to another inference point in your model for one dimension, but need to declare the other dimension.

In fact, all drawing and modification tools have the ability to accept input from the user. Each tool is slightly different in what it will accept for input. Check out the full list here. Circles and polygons also let you feed a radius ( 10’r ENTER) and the number of segments (12s ENTER). The Arc tool is similar. The Push/Pull tool, Move tool, Offset tool,  Scale tool also allow such an input to determine the length of the modification.

The most complicated one is the Rotated Rectangle tool. You can check out my complete flowchart of optional user input in my Rotated Rectangle tutorial.

Once you move on, you lose your opportunity

The thing that trips people up is that once you’ve moved onto a different tool, you lose the opportunity to change the dimensions of the action you just performed. So if you draw a rectangle, you can change its dimensions all day long… as long as you don’t activate a new tool. As soon as you pick a different tool, you can no longer type in a new dimension for the length and width of the rectangle.

This is usually the point at which some people declare SketchUp is inaccurate and doesn’t let you change the sizes of things, as they go searching for the “rectangle properties”.

But, they are wrong. There are still plenty of ways to modify entities in SketchUp. You just need to change your frame of mind a little. Just realize that everything in SketchUp is ultimately an edge, or a surface. SketchUp doesn’t really recognize a “rectangle.” The rectangle tool is just a shortcut way of inserting four edges and a connected surface between them. Just as the Push/Pull tool is a shortcut way of  adding 5 surfaces and eight edges to a rectangle, in order to make a “cube”. You could draw them manually with the line tool, but SketchUp provides tools to make it easier.

Once you’ve drawn the rectangle and moved on, you need to look for other ways to modify the entities you now have in your model.

The Move tool

Using the Move tool, you can change the position of any selection of entities, in any direction, with precision.

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Clik here to view.If you know the distance you need to move an entity:

1. Select the entity or entities with the Select tool (Spacebar). (Either click, or click & drag)
2. Activate the Move tool (M), click once to start the move.
3. Tap an arrow key on your keyboard to lock axis (Left = green, Right = Red, Up = blue)
4. Move the mouse towards the direction you want to move, and click at a random position. (It doesn’t matter how far you move it, you just need to get the direction of the movement correct.)
5. Type in the precise distance you want to move the entities, and press ENTER. (The entities with then reset to the exact position you specified, along the direction you moved them.)
6. Repeat the move if you need to move the entities along a different axis in order to get them to their final location.

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Clik here to view.If you don’t know the distance you need to move an entity, you can use the Tape Measure tool to place a guide.

1. Activate the Tape Measure tool (T). Click on an edge that you’d like to measure a distance from to create a guide. (Make sure you click along the edge, not on an end point, or else it won’t create a guideline.)
2. With the Select tool (Spacebar), select the entity you’d like to move.
3. Activate the Move tool (M). Snap to an end point of the selected entity, then move it towards the guide until you snap to it. Click again to finish the move.

Using guides to help you move entities allows you to move precisely without knowing the actual length of the move, but instead, placing a guide to where the entities need to end up from a known dimension. You can still use arrow keys to lock axis during the move in order to confirm you are moving along one axis at a time.

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Clik here to view.If the distance is relative to another object within your model, you can use it to help you align and measure the movement.

1. Select the entities you’d like to move.
2. Activate the move tool. Click on the first point in your model you’d like to reference for the move. (This point doesn’t need to be connected to the selected entities that are about to be moved.)
3. Click a second point in your model that you’re using to reference for the distance of the move.

To learn more tricks about the Move tool, check out my other article, 10 tricks for the Move tool in SketchUp. As you can see, the SketchUp inference system plays a vital role in this too, you can check out my article on the inference system here.

The Scale tool

The Scale tool is also really helpful for modeling with precision in SketchUp. The scale tool is most commonly used on groups and components, but it can be used an any selection of entities, from a single face, to a selection of multiple faces.

By default, you have to type in a scale factor in order to define the distance you want the scale tool to move entities. But you can also feed a dimension to the Scale tool, and it with scale the selection to match the overall dimension.

To scale a selection to a precise dimension:Image may be NSFW.
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1. Use the Select tool to create a selection.
2. Activate the Scale tool (S), and click on one of the handles to start scaling.
3. Click again to finish scaling, then type in the actual dimension you want the selection to be scaled to and press ENTER.

If you’d like to learn more tricks about the Scale tool, check out my article 8 tips for scaling in SketchUp.

A word on precision

SketchUp is 100% precise. When you type in a dimension into the VCB, SketchUp will draw or move the entity to that exact location. (I don’t know if there is an actual limit to the level of modeling precision, but I’ve never hit it.) For example, I can draw a guide at 1/1024th of an inch from another guide, and SketchUp will place it precisely at 1/1024th.

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But nobody ever models to that level of precision, so SketchUp has enabled some settings that will only display units as close to the level of precision that you define. If you go to Window -> Model Info -> Units, you can change the unit of measurement that SketchUp will display in the VCB. This will define the highest level of precision that will be displayed. This does not change the size of your model in any way.

If you drew a rectangle, 10′ by 10′, then changed the Model Unit to millimeter, the rectangle would still be 10′ by 10′, but when you measure it with the Tape Measure tool (T), the VCB would display 3048mm instead. (10 feet = 3048mm).

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With the level of precision set, if you try to measure something that does not land exactly on an interval of the highest level of precision, you’ll see a ~ character before the dimension. This tells you that it’s close, but not exactly at that measurement.

Note: Length snapping will set the interval at which the cursor will snap to measurements. I rarely rely on this since I prefer to type in my dimensions for action I take.

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For example, if I were to set my display unit precision to 1/8″, and tried to measure a distance of 3/32″, it would display ~1/8″.  The maximum level of precision for display units is 1/64″, and 0.000000mm

I hope this has cleared up some confusion, and taught you some basics on how accurate SketchUp really is. If you have any questions or comments, leave a comment below.

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