# Dispersion in Chromatography Columns - The Van Deemter Equation > Page 63

The column lengths necessary to achieve these efficiencies can be calculated employing equation (44). The results obtained are shown as curves relating maximum column length to particle diameter in figure 13.

**Figure 13.
Graph of Log. Column Length for Maximum Efficiency against Particle Diameter**

It is seen from figure 3 that the column length ranges from just under a centimeter, which provides an efficiency of about 3500 theoretical plates to nearly 70 meters which provides an efficiency nearly 1.5 million theoretical plates. Seventy meters is a long column, but not an impractical length. The question remains is how long will the separation take?