Abstract: In a flow cytometer where the laser beam is larger than the size of each biological cell of a column of cells being passed through the laser beam at a high rate wherein new and improved method and means are used to calculate the size of the cells as sensed by low angle forward light scatter or secondary emission of fluorescent material on the surface of the cell by measuring the time-of-flight of the smaller cell across the laser beam, with the time-of-flight being measured by integrating an electrical signal from either the forward light scatter or the secondary flourescent emission from a single cell as it passes through the laser beam and deriving still another electrical signal measuring the peak amplitude of the first signal and then dividing the integrated signal by the peak signal and subtracting a constant electrical signal from that quotient.