Converting Imperial to Metric and Metric to Imperial

To convert from imperial to metric multiply the length, in inches, by 25.4 (the number of millimeters per inch).

Example: 3 inches converted to millimeters is 3*25.4 or 76.2mm.

To convert from metric to imperial multiply the length, in millimeters, by 0.03937 (the number of inches in a millimeter). For greater accuracy use 0.03937008.

Example: 100 millimeters converted to inches is 100*0.03937 or 3.937 inches.

Hi ReMark....if I may add something....and I don't know if all versions of autocad support this...

if you enter -dwgunits (with the dash...and maybe -aecdwgunits for some) you will be able to not only scale the drawing from one unit to another, but also change the actual database units (which is important in my opinion).

Here is a sample from my command line as I changed from Feet to Meters:

Command: -DWGUNITS

Drawing units:

1. Inches

2. Feet

3. Millimeters

4. Centimeters

5. Decimeters

6. Meters

Unit for length : 6

Drawing unit display formats:

1. Scientific

2. Decimal

Linear display format :

Linear display precision :

Scale objects from other drawings upon insert? [Yes/No] :

Match INSUNITS to drawing units? [Yes/No] :

** WARNING: you have changed the unit for this drawing database. **

** All new objects will be drawn according to the new unit, but **

** existing objects will not change size unless you specifically **

** ask to have automatic scaling occur. **

Scale objects in current drawing to reflect change in units? [Yes/No] :

Include objects in Paper Space? [Yes/No] :

Scaling the entire database...

Scaling AecDbObject(s)...

Scaling entities in Model Space...

Scaling entities in Paper Space...

Cheers.

That is a good point. Thanks for bringing it to my attention.

Hi ReMark....if I may add something....and I don't know if all versions of autocad support this...

 

if you enter -dwgunits (with the dash...and maybe -aecdwgunits for some) you will be able to not only scale the drawing from one unit to another, but also change the actual database units (which is important in my opinion).

Here is a sample from my command line as I changed from Feet to Meters:

 

Command: -DWGUNITS

Drawing units:

1. Inches

2. Feet

3. Millimeters

4. Centimeters

5. Decimeters

6. Meters

Unit for length : 6

Drawing unit display formats:

1. Scientific

2. Decimal

Linear display format :

Linear display precision :

Scale objects from other drawings upon insert? [Yes/No] :

Match INSUNITS to drawing units? [Yes/No] :

 

** WARNING: you have changed the unit for this drawing database. **

** All new objects will be drawn according to the new unit, but **

** existing objects will not change size unless you specifically **

** ask to have automatic scaling occur. **

Scale objects in current drawing to reflect change in units? [Yes/No] :

Include objects in Paper Space? [Yes/No] :

Scaling the entire database...

Scaling AecDbObject(s)...

Scaling entities in Model Space...

Scaling entities in Paper Space...

 

Cheers.

This is an outstanding addition to the ongoing dialogue about scaling and drawing units of measure/measurement systems!

I am quite surprised to learn that there IS a way to change the database units, as I was quite sure there was not.

I have used the -AECDWGUNITS command before, but had not noticed that this dialog provides a way to do just that.

Excellent, I used to copy to a fresh blank template of the database units I wanted.

To convert from imperial to metric multiply the length, in inches, by 25.4 (the number of millimeters per inch).

Example: 3 inches converted to millimeters is 3*25.4 or 76.2mm.

To convert from metric to imperial multiply the length, in millimeters, by 0.03937 (the number of inches in a millimeter). For greater accuracy use 0.03937008.

Example: 100 millimeters converted to inches is 100*0.03937 or 3.937 inches.

For converting metric to imperial, I tend to use fractions for precision. Very easy to use for scaling. Since we know that 1" = 25.4mm, I enter at the prompt: 10/254

When entering a length, I adjust the fraction /254 depending on decimal places and add zero's as required since fractions don't like decimals. In your example of 100mm, I'd enter: 1000/254. If it was 100.5mm, I'd enter: 1005/254. If it was 100.57mm, I'd enter: 10057/2540. This guaranties perfect precision... as long as you don't mess up the zero's.

Changing the units is fine only problem is that when you go from feet to meters you shave bits the sizes are not the same if you drew 3" = 76.2 you would specify 75mm because thats what the metric manufacturer would actually supply, a good example concrete drianage pipes the manufacturers did not change their moulds but a 1' pipe is now 300mm if you measure its 304mm but when it comes to plastic it can be truly MM size or a imperial convert.

Just threw in these comments as if you are use to dwg in feet and have to design metric need to make sure of the foot/metric sizes. Just had a look at a local steel supplier and their tubes are a mix of imperial and metric eg sq tube 1" = 25.4, ok 2"= 50mm not 50.8 other sizes a real mix like 50x25 next size 50.8x31.8

My choice of topic and thus the reason for this thread was to address the many questions we seem to get regarding receiving a drawing done in one unit and wanting to change it to the other. But you all have brought up good points and for that you have my thanks.

Scaling from Imperial inches to Metric millimetres by multiplying by 25.4 is 100% accurate.

To achieve 100% accuracy when scaling millimetres to inches I use a toolbutton with this macro: -

^C^C_select \scale p; \r 25.4 1