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How to change units


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#1 Carlos Lima


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Posted 11 May 2023 - 08:58 PM

How do I change the drawing unit?
My system is in millimeters and I need to put it in inches.

I already accessed the Units screen, changed the box to inches, but nothing changed.
The drawings remain with the same measurements.
For example, making a line of 100 units of millimeters is the same dimension as a line of 100 units of inches.

#2 David Duncan


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Posted 18 May 2023 - 01:17 AM

You might be confusing 'units' with 'scale'. It's one thing to change the drawing units from one type to another... it's another thing to adjust the scale of the object to reflect the drawing units desired. You may already understand this but bear with me.
Example: Units = Decimal. Construct a line that is 100 units long. Use 'DI' (Distance) to confirm the length, or use a dimension to measure (assuming the dimension type is also set to Decimal). The line will be 100 units long, as you point out. You can also confirm the lengths in the Properties box.
Now change the units to be 'Architectural'. Repeat the DI or dimension. The length should show as 8'-4". Still equals 100.
These settings are fine, as long as you haven't generated any objects on the drawing. You just need to make sure the units and dimension style setting match and away you go.

The problems occur when you have an existing drawing created using one unit type and you want the drawing in another type. This is where you need to scale the drawing up or down depending on dimension values you want. A line that is 100 mm long is 3.937 Imperial inches long +/-. To achieve this, the existing line is scaled using the SCALE command and a scale factor of .03937. This number is the inverse of 25.4, or 1 / 25.4
So, if you have a drawing, you select the entire drawing (model space only) and use SCALE to adjust the relationship between metric and imperial. The same is true in reverse except for the scale factors.

The easiest method I know to make these adjustments quickly and accurately is to scale the drawing using a known dimension... whether that be a doorway or part or other component you are sure of. For me, being a space planner / designer, I know what door widths are so that's the component I use as my scale reference.
If the existing drawing is in metric, I find a door that I can measure accurately and one that I know the size of in imperial. For this example let's set the door width to be 3'-0" / 36". I change my drawing unit to Fractional or Architectural, adjust my dimension settings to give inches or feet / inches. Then using SCALE, I select the components I want to adjust, then select the base point using one side of the door, press 'R' for reference length, select the opposite side of the door using a constraint so it's parallel, then enter in the length I want. In this case 36. If I've done everything correctly I should now have a drawing that has been scaled from metric to imperial, and all the proportions are correct. You can continue using this method until you have the drawing scaled to whatever accuracy you need. This is actually a lot harder to describe than to demonstrate.

I hope this helps you out and answers the question.

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