Excel’s convert function works well to convert between simple units. However, in engineering, there’s often compounds units where simple units are either multiplied together or divided by one another.

One example is the units for torque, where we multiply a force times a distance (i.e. N*m). Another is the units for specific energy, where we divide units of energy by units of mass (i.e. kJ/kg).

The convert function cannot deal with these compound units directly, but it’s fairly easy to work around that limitation to work with compound units.

In the “Compound Units” tab of Worksheet 03u, there are conversion for both torque and specific energy. We’ll combine two **CONVERT **functions to handle these conversions. To convert the torque, we’ll begin the formula as usual:

** =CONVERT(C4,
**

This first **CONVERT **function will be used to convert pounds force (“lbf”) to Newtons (“N”). You can’t select the units in the cells; instead, type them in as we did in the beginning of the last section. Don’t forget to use double quotes around each unit.

**=CONVERT(C4,”lbf”,”N”)
**

Next, we’ll multiply by another **CONVERT **function to convert from feet to meters. Add an asterisk (*****), then **CONVERT**. Don’t enter the cell C4 again, however. Simply use the number 1 as the first argument.

**=CONVERT(C4,”lbf”,”N”)*CONVERT(1,
**

Next, add the units:

**=CONVERT(C4,”lbf”,”N”)*CONVERT(1,”ft”,”m”)
**

This is the Excel version of an equation with two conversion factors, i.e.:

Often, engineering quantities call for a unit that is divided by another unit. The conversion for specific energy involves an energy divided by a mass. We can do this conversion similar to the multiplication above by substituting a forward slash (**/**) to divide the units. For the second example, the formula will begin:

** =CONVERT(C7,”kJ”,”BTU”)
**

Add a forward slash, then a **CONVERT **function for the mass units:

** =CONVERT(C7,”kJ”,”BTU”)/CONVERT(1,”kg”,”lbm”)
**

This CONVERT function is equivalent to the mathematical equation:

Using Excel to convert between complex units is fairly straightforward. Remember to only include the number that’s being converted in one of the CONVERT functions, and to use the number “1” in additional CONVERT functions.