We investigated a method for calculating polychlorinated biphenyl (PCB) concentrations in indoor air from the amounts trapped in passive air samplers (PASs) by yarns as trapping materials in order to establish a practical and simple monitoring method. To determine the coefficients required for the calculations, indoor air sampling by yarn PASs and low-volume air samplers was conducted in laboratories over 2 months. The uptake coefficient was determined by dividing the rate of increase in the concentrations of the compounds in the yarn SAS by those atmospheric concentrations measured by a low-volume air sampler. The elimination coefficient was calculated as the ratio of the concentration in the PAS to the atmospheric concentration under equilibrium conditions over 2 weeks. An advantage of this method is that if environmental conditions (air temperature, humidity, wind speed, etc.) do not vary greatly then the atmospheric concentration can be calculated by using a single equation at any place and any time, even when adsorption by the yarn SAS ha not reached equilibrium. The calculated atmospheric concentrations of PCBs were within the range of two to three times the concentrations measured by active air samplers (AASs) at 23 to 28 °C.