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Understanding the Metric Measurement System

Updated on November 12, 2013

Inches v. Metric

For many years I have heard people here in the USA complain about how difficult it is to convert Inches to Metric and Metric to Inches. It involves a bit of math and the results are rarely even in either system.

For example the standard Inch measurement of 3/16” = 4.7625mm. You cannot find a Metric drill bit 4.7625 mm that will drill a 3/16” hole. That size is not available. The closest you can find is a 4.5mm.

4.5mm = 0.1772
3/16 = 0.1875

However 4.5mm makes a dandy clearance hole for a 4mm shaft.

Change the way you are thinking

Thinking in Inches is a major disadvantage. Thinking in fractional inches is pure suicide. The machine shops that work in Inch units will use decimal inches. 1/16” = .0625”. This makes sense because your digital readouts go out to four decimal places or more, but fractional inches are not practicable for Metric conversion. Remember when NASA lost a $125 million Mars Orbiter because one group used Metric units and the other used English units? Oops. Face it, the Metric system is here to stay and is found everywhere nowdays. It is better to understand and learn how to use it.

Helpful tips

To get a proper handle on Metric you first must:

  • Get rid of fractions. Never use them for anything. Get used to never using them.
  • Stop thinking in Inches. Period. Inch and Metric measurements are numbers. If you can think of it in those terms, you are most of the way there.
  • Learn from looking at a Metric scale the sizes of standard Metric measurements.

Find your inner child

How did we learn Inches growing up? By seeing what size something was and using an Inch scale to measure it. Remember, these are just numbers. You want to be able to look at a distance and say that is about 2 centimeters on your Metric scale. Soon you will be able to say, ”My guitar is about a meter long,” “A dime is about a millimeter thick,” “My thumbnail is about a centimeter wide.”

We hold up our hand with a gap between our thumb and forefinger and say it’s yea big. How big is a “yea?” It’s about 25 mm.

You will soon get the rough feel for the measurements and will be able to estimate the size of something using the Metric system.

The biggest point I'm making is that you have to dive in and fully immerse yourself in Metric measurements to really understand them.

Come on in, the water is fine.

Later we can discuss temperatures and speed measurements. This is enough for now.

A Dime is Just Over A Millimeter Thick
A Dime is Just Over A Millimeter Thick
Yea Big
Yea Big

Inches or Metric

Which system of measurement do you prefer?

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