During metal machining the rotating machine tool or grinding wheel is generating fine droplets and vapor which can cause occupational health problems. A new continuous measuring method was developed to detect both droplets and vapor of metalworking fluid mist and to provide information about the droplet size distribution. According to this method, an air sample of the metalworking fluid mist is segregated by impactors of different cut sizes, carried out in several successive passes. In each pass the droplets that are not collected in the impactor are fed into an evaporator that immediately evaporates all droplets, and subsequently the sample is analyzed in-line by a Flame Ionization Detector (FID). By subtraction of the value measured at the respectively next smaller fraction, the oil amount of the metalworking fluid mist found in a certain droplet size range is obtained. The metalworking fluid mist is thus segregated according to the droplet size, and a definite cut size between droplet and vapor can be defined, below which we can say "vapor". This method was calibrated with Di-2-Ethylhexyl-Sebacat (DEHS) as equivalence substance for further measurements applied on various metalworking fluids.