Different unit systems are allowed for user input. Most input parameters have multiple units which are commonly used in industry. An instantaneous unit conversion is featured that instantly gives the correct values corresponding to the units chosen.

The units associated with each input are listed below in the table.

Parameters	Units in the user input	Units in the model calculation
Temperature	°C, F, K	K
Pressure	bar, psi	bar
Diameter *	m, cm, inch	m
Velocity	m/s, ft/s, rpm**	m/s
CO2	bar, psi, %mol	bar
Fe2+	ppm(w)***, M	ppm(w)
HAc	ppm(w), M,  %w	ppm(w)
O2	ppb(w), ppm(w)	ppb(w)
H2S	ppm(g)****, bar, psi, %mol	ppm(g)

*: use specimen diameter for glass cell system and pipe diameter for pipe system.
**: use m/s and ft/s for pipe system and rpm for rotating cylinder system.
***: w denotes in water phase.
****: g denotes in gas phase.

Although different units can be used for input, a default unit is employed in the model for each parameter, as indicated in the table above. The units that are used in the corrosion model are also shown in the table. For fluid velocity user may enter diameter and velocity values for the corrosion prediction in pipe systems, or diameter and number of revolutions (rpm) for small laboratory equipment such as glass cell or similar (in the latter case FREECORP calculates fluid velocity).