Mathcad Units and Unit Conversions

When you first start Mathcad, a complete set of units is available for your calculations. You can treat these units just like built-in variables. To assign units to a number or expression, just multiply it by the name of the unit.

By default Mathcad uses units from the SI unit system. in the results of any calculations.

Units can be typed or selected by choosing Unit from the Insert menu.

Mathcad will automatically check for proper units and do conversions.

DO NOT NAME YOUR VARIABLES WITH COMMON UNIT NAMES - naming a variable kg or m will cause problems.

Here the mass is defined for a problem. The unit kg is added to the definition by multiplication.
Type: mass:25*kg


The same procedure is used for the acceleration.
Type: acc:9.81*m/sec^2

Then we define the force as F.

Typing F= where the ordinary equal sign is used yields the result of the calculation including units. Whenever units are used to define a variable then units are produced in the answer.

The calculation is now extended to include momentum. Notice the time unit.

Units are important for checking equations to be sure a derivation is correct. If units are incompatible then Mathcad will give you an error message.

Unit Conversion

There are two ways to convert from one set of units to another:

- by using the Insert Unit dialog box, or

- by typing the new units in the units placeholder itself.

Click the unit you want to replace and chose a unit from the Insert menu, or edit the unit placeholder directly by typing a new unit or any unit expression, like in² or 1/sec .

Here is an example:

If we define a variable in gallons, Mathcad will automatically displays its value in m³.

To see this value in in³, click on the units placeholder and type in in³

Click outside the expression to redisplay the result in terms of the selected units.