# Imperial measurements [closed]

I am studying electricity, electronics, and electrical engineering.

Could somehow show me how to use the below pictures, which cover conversions? I know it is showing conversions for metric and imperial, however I am struggling to make sense of the rulers.

Some simple practical examples would be sufficient.

• look at a tape measure or at a ruler that has both inches and centimeters Commented Aug 2 at 0:23
• securityauditor - Hi, Where did the images come from? To comply with the site rule on referencing, details of the original source of copied / adapted material must be provided by you, next to each copied / adapted item. If the source is offline (e.g. book, as it seems in this case, or private intranet) then edit the question and add full source details e.g. title, author, page, publisher, edition. If the original source is online & public, please edit the question & add the webpage/PDF name & its link (URL) (e.g. website name + webpage title + its URL). TY Commented Aug 2 at 0:47
• I’m voting to close this question because it has nothing to do with Electrical Engineering. Commented Aug 2 at 3:52
• @brhans, physical dimension measurements are part of electrical engineering. So is units conversion. The method may be only of historical interest but it's not off-topic. Commented Aug 2 at 12:40
• This question is probably on-topic at Engineering Stack Exchange. Commented Aug 2 at 13:24

Simply draw a horizontal line (or use an edge) at the measurement of interest and read off the conversion.

In the screengrab above I want to convert 15/64" and I can see that it is almost exactly 6 mm or 24/100" (0.24").

The inch was redefined as exactly 25.4 mm (in 1956, if I remember correctly) so the mathematical conversion is $$\ \frac {15}{64} \times 25.4 = 5.953125 \ \text {mm} \$$ and $$\ \frac {15}{64} = 0.234375\ \text{inches} \$$.

• Lovely answer! Could you explain the very last part where you converted 15/64 into 0.234375 inches? I know from looking at the diagram that your answer looks right (it is just under 24/100") but how did you get such an accurate answer of 0.234375 inches? :-) Commented Aug 3 at 2:50
• I simply divided the fractional inch value out to convert to decimal. At the risk of giving you a face-palm moment: In the same way that 3/4" = 0.75" (just divide 3 by 4), 15/64" = 0.234375" (just dividing 15 by 64). Commented Aug 3 at 9:49

As we know,

1 inch = 25.4 mm (1" = 25.4 mm)

In the first page, in 3 left-hand side rulers, we may read that basic relation at their topmost edges:

100/100 of inch (1st ruler) = 25.4 mm (2nd ruler) =
64/64 of inch = 32/32 of inch = 16/16 of inch = 8/8 of inch (3rd ruler).

(The other 3 rulers, in the right-hand side of the same page, are only detailed view of the bottom part of those left-hand side rulers.)

64, 32, 16, 8

mean fractional units, i.e., in those columns you may see the number of 1/64, 1/32, 1/16, 1/8 of an inch, respectively.

In the second page,

• the middle ruler is the same as the first ruler in the previous page, but symmetrically expanded to the right — for a convenient comparison with ticks on

• the right-hand ruler, i.e., with hundredths of an inch.

• the left-hand ruler has columns colored identically with colors in the middle ruler, but instead of fractional labels on their ticks e.g.,

• 10 in the green column labeled as 16, which means 10/16 of an inch, or
•   5 in the yellow column labeled as   8 in the same tick, which means 5/8 of an inch,

they are labeled with decimal numbers, particularly .625 in our example (because 10/16 = 5/8 = .625).

• I love youuuu thanks soooooo very much! :-) Commented Aug 3 at 3:11

To use them, just hold something with a straight edge horizontally on the tickmark of the measure you know, and then follow it to the corresponding unit you want to convert to.

jstola posted a good example in the comments, a dual inch/cm tape measure is not unusual:

#### But…

You don't use them. No one would. That's why there aren't really any practical examples. It may have been useful 40 years ago but I have no idea why it's still published in something else than a history book alongside slide rules and a picture of a valve manufacturer's catalogue.

First of all, I've never seen "hundredths of an inch" used in electrical engineering, the common units are:

• inch (circuitboard length/width)
• mm (mostly everything)
• mil/thou, thousandths of an inch (PCB track width, component pitch)
• µm, micrometer, thousandths of a mm (copper/plating thickness)

But you never need to do accurate conversions between these without access to something that can calculate it for you.

You need to know the basics to make simple order-of-magnitude calculations and to check if things make sense: 25.4 mm in an inch, 1000 mil in an inch, 1000 µm in a mm. The rest you'll learn by experience when needed.

• pipe - Hi, Please add the required reference to the source of that image e.g. website name + webpage title + URL (link). TY Commented Aug 2 at 0:49
• @SamGibson Shouldn't the direct link to the source fulfill all those requirements and more?
– pipe
Commented Aug 2 at 1:21
• pipe - No. Unless you add the reference here according to SE rules, you are giving the false impression that the answer (including the image) is all your own work (which it isn't). It's unreasonable (and not required by SE) for readers to figure out the image source. Whether you link to the original source directly, or copy the image to SE servers, makes no difference to the referencing requirement. Right now, people will look at your answer and see no other source reference, meaning you're claiming it's yours - hence the reference is needed, to avoid plagiarism. Commented Aug 2 at 1:42
• (To make things even more complicated, that Wikipedia / Wikimedia Commons image has a CC BY-SA 4.0 license which adds extra obligations on you, to comply with its license - although few people understand or follow the license terms correctly.) Commented Aug 2 at 1:43