An infusion pump, including: a microprocessor a drip chamber a drip tube with an end in the drip chamber and an illumination system: with a light source for transmitting light through the drip chamber to a drop of fluid suspended from the drip tube and for controlling illumination properties of the light transmitted to the drop. The pump includes an optical system for: receiving light transmitted through the drop and transmitting, to the microprocessor, data regarding the received light. The microprocessor: generates, using the data, an image of the drop locates, using the image, an outer edge of the drop to define a boundary of the drop integrates an area enclosed by the boundary and calculates a volume of revolution for the drop with respect to an axis for the drop that intersects the end of the drip tube, assuming symmetry of the drop with respect to the axis.
