Unit Conversions

One of the most critical elements of problem solving in engineering, besides identifying the problem and exploring solutions, is to be able to accurately calculate quantities in the proper units of measure.

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Converting inches to feet, miles to meters, gallons to liters, hours to seconds, nickels to dollars are some of the many types of conversion problems that we often face.

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In order to properly set up a unit conversion equation there are three basics types of information or variables that we need to identify.

They are:

Knowns (Given or Have), Unknowns (Want or Need to find), and Conversion Factors (Constants that relate one variable to another)).

Once that information has been identified and segregated, we need to set up the equation.

Unknown = (Known) x (Conversion Factor)

It is important to set up the equation where the final answer is expressed in the desired units, and where the undesired units are cancelled out.

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Conversion factors are found in tables, charts and in several sites on the internet.

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The following step-by-step procedure can be used to solve any unit conversion problem:

Steps for unit conversions

1. Write out the units you have (when appropriate as a fraction):
2. Write out the units you want to end with:
3. Determine appropriate conversion factors (in some cases, there will be more than one conversion factor for each of the units you have):
4. Evaluate appropriate arrangement for fractions (that is, what units belong in numerator (top) of fraction? What units need to be in denominator (bottom)?
Remember, units cancel when one unit is in numerator and the other is in the denominator). Remember that when you multiply fractions (as you will in step below), you can cancel units ONLY when they appear in both the numerator and
the denominator.
5. Set up the conversion by writing the fractions in a row with multiplication signs in between
6. Evaluate. Do the original units cancel so that you are left with ONLY the units asked for? If not, repeat steps 3 and 4 until you are left with appropriate units:
7. Multiply across top and bottom:
8. If necessary, reduce the fraction.
9. Evaluate your answer.

Example: Convert 15 inches into feet.

Known: 15 inches, Unknown: X feet, and Conversion Factor: 12 inches = 1 ft, or       (1 foot / 12 inches).

Equation:  (15 inches) x (1 foot / 12 inches) = X feet

By cancelling out inches, and dividing 15 by 12, we get: 1.25 feet as our final answer.

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As you can see, it is easy to convert units, as long as you follow the simple process outlined earlier. Please note that units can fall in several categories as depicted by the graphic above. Angles, Area, Energy, Length, Speed, Power, Volume, Times, Rate, Temperature, are some of the many quantities and measurements that can be calculated.

In case you did not follow that approach, and still have questions on how to convert units; below you will find a few YouTube videos that will attempt to explain the same concept with different variations to the approach.

Check them out and find the one that makes the most sense to you.

Here is another link that you may want to visit:

What do you think? Did you find a lesson that fits your learning style? Did you get the idea and the concept of Unit Conversion? We hope so.

Now that you have learned the basic principles of unit conversion, is time to practice and see how good you really are.

The following conversion factors will come handy whenever you need to find out the relationships between various constants.

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The website below gives you a few problems to test your newly acquired skills. Copy and paste to your browser.


You can also test your knowledge by using the Quizlet website below to try out a few practice problems. You can also use the flashcard option to review.


You are now an expert, and it is time to take a final assessment and see if there is anything more that you need to practice, before you can move on to the next STEM topic.

Copy and paste the following Quizlet link to your browser and see how good you really are. If not that good yet, keep practicing and taking the assessment until you reach a 90% rate or better. Good Luck!!!!!


Hope you were able not only to learn and practice the concept of Unit Conversion, but we also hope that you found the lesson to be effective (fitting to your learning style) and most of all, FUN.

Great Job!