Introduction to units and dimensions

NASA Spaceshuttle

This article will review several systems that expresses units and dimensions in a different way. A brief introduction to the imperial, US customary, metric and SI system will be given. Continue reading to learn more about these systems.

Importance of knowledge

Did you know that NASA once crashed a Mars Orbiter due to a mix up in the units of measurement?

How could this happen?

The NASA engineers were working with both the imperial and metric system of units. This caused mistakes leading to the crash of the Mars Orbiter. Hopefully, something like that will never happen to you after reading this article.

Also, knowledge of units and dimensions gives you much more options in life.

Large parts of the engineering data out there is (or was) measured in different units than you are used to. Try searching on engineering toolbox and sooner or later you will come across an article you can’t use because you don’t know the units.

Your world will be so much bigger if you know more units to measure that size in. Whether you measure it in meters, inches or furlongs.

A recent study showed this:

Knowledge chart

Knowledge chart

This was a joke (just in case)

What systems are there?

A unit of measurement is basically a definition of magnitude and quantity. But the way how to define these is not universally agreed upon.

Imperial system

First of all there is the imperial system of measurement that originated from the British empire. The countries on the British Isles mainly converted to the metric system but some units of the imperial system are still in use.

US customary system

Secondly, there is also the US customary system. This system originated from the imperial system due to the colonial history of the United States. The imperial and US customary system are different from each other because of some changes in later history.

There are for example different ways to express the weight in ton, namely the US ton and UK ton. Also, the metric system uses tonne for weight measurement. That’s why it is important to always be specific in your unit quantities.

Metric system

This system finds its origin in the French Republic of Napoleon and is the most used system of measurement. The metric system uses decimal multiples to express units. This means the units scale up and down in multiples of 10. Many of the standard units in the metric system are the same as in the SI system.

International system of units

The international system of units (SI) is the modern form of the metric system and is used in scientific documentation. It is built on 7 base units:

  • kilogram (kg) for mass
  • meter (m) for length
  • second (s) for time
  • kelvin (K) for temperature
  • mole (mol) for amount
  • ampere (A) for electric current
  • candela (cd) for luminous intensity

The SI units system will be used for the engineering calculations in this blog.

Length measurement

Further reading

In this articles we have shortly introduced the imperial, US customary, metric and international system of units. In upcoming articles we will review the differences between these systems in measuring specific quantities like length, mass and volume.

I hope this article got you motivated to learn more about units and dimensions. Click the link in the box below for articles about units and dimensions.

If you like to read more about the history of units and measurement I can recommend the “Encyclopedia of scientific units, weights and measures” written by Francois Cardarelli. It’s a very good book that learned me a lot about units and dimensions.

Coulson and Richardson volume 1 “Fluid flow, heat transfer and mass transfer” chapter 1 and Perrys “chemical engineerings handbook” section 1 also covers this material.

Share your views

How do you feel about the several units of measurement? Which system do you prefer? Please share your thoughts in the comment section below 🙂


@ Engineerings fundamentals

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