In practice, the osmotic pressure produced by an ideally dilute solution would be too small to be accurately measured. For accurate  measurements, solutions are not ideally dilute and a virial equation is used to account for deviations from ideal behavior and allow the calculation of . The virial equation takes a form similar to van ‘t Hoff's law of osmotic pressure, but contains additional constants to account for non-ideal behavior:
where  are constants and  is still the concentration of polymer 1. This virial equation may be represented in different additional forms:
where  and  are constants and .