Equations were derived for calculating dilutions in vented cigarette filters and tobacco columns from pressure drop measurements. These calculated dilutions are found to agree closely with those directly measured for a variety of commercial and experimental cigarette wrapped with perforated and porous tipping and with different cigarette papers. The effect of hole placement on dilution and cigarette pressure is estimated. The effects of filter dilution on particulate matter, condensate and carbon monoxide delivery are discussed. A method for measuring filter dilution during smoking by means of pressure drop measurements is outlined and results for a typical vented filter cigarette are shown and discussed. The use of pressure drop measurements for estimating paper porosity and amount of dilution in the tobacco column on finished cigarettes is outlined. The dilution obtained by this method was generally higher compared to the results found by a model based on a capillary flow regime, which suggests that flow through ordinary cigarette paper is a combination of capillary and orifice flow. The non-destructive nature and simplicity of pressure drop measurements make this method of measuring dilution useful in quality control of cigarette production.