PTC Mathcad provides a complete set of units in the International System (SI), United States Customary System (USCS), and Centimeter Gram Second (CGS) unit systems. You can specify values using these built-in units or using your own user-defined units. Tables, plots, matrices, and math regions take units. Most built-in functions take units when it is logical. For example, you can add units to a data set and find its average value using the mean built-in function, but you cannot calculate the sine of 2 kg.

In PTC Mathcad, all variables are displayed in the unit system of the worksheet. For example, to measure the volume of a sheet of aluminum foil, you can define its width to be 30 cm, its length to be 1 m, and its thickness to be 10 μm. When you evaluate each of these variables, the result is 0.3 m, 1 m, and 0.00001 m respectively in the SI unit system. You can then calculate the volume of the sheet without concern about the units of the variables, the result is 0.003 L.

As a best practice, always include units when you define variables if they are relevant. For example, if you define velocity to be 100, and time to be 0.5, PTC Mathcad cannot perform unit checking or unit balancing when you calculate the distance. It is a better practice to define the velocity as 100 km/hr and the time as 30 min. It can also prevent errors later on.

You can change the displayed units of any calculation result to suit your needs. When you modify units and recalculate the worksheet, PTC Mathcad performs automatic unit checking to ensure that the units remain mathematically correct.

Pay special attention when working with temperature units. PTC Mathcad distinguishes between absolute temperatures, such as room temperatures in degrees °C or °F, and a rise or fall in those temperatures, measured in Δ°C or Δ°F.