A particle quantifier includes a filter with a predetermined number of pores of a first predetermined size, a pump, and a fluid path from the pump to the filter. A pressure sensor is responsive to fluid pressure in the fluid path, and a processing module is responsive to the pressure sensor. The pressure increase of a sample fluid in the fluid path is determined as it is pumped through the filter and particles in the fluid are trapped by the filter. This pressure increase is compared with calibration data and an estimate is made concerning the concentration of particles greater than a second predetermined size present in the sample.