| Description | Symbols |
| Feed rate [Kmole/min] | F |
| Feed composition [mole fraction] | zf |
| Fraction of liquid in feed | qf |
| Distillate (top) and bottom product flow rate [Kmol/min] | D and B |
| Distillate and bottom product composition (usually of light component) [mole fraction] | yd and xb |
| Reflux flow [Kmole/min] | L |
| Boilup flow [Kmole/min] | V |
| Number of stages (including reboiler) | N |
| Total number of stages (including condensor) | Ntot = N |
| Stage number (1-bottom, NF -feed stage, NT -total condensor) | I |
| Liquid and vapour flow from stagi [Kmole/min] | Li and Vi |
| Liquid and vapour composition of light component on i | xi and yi |
| Liquid holdup on stage i [Kmole] (MB-reboiler, MD -condenser holdup) | Mi |
| Relative volatility between light and heavy component | Α |
| Time constant for liquid flow dynamics on each stage [min] | τL |