This paper introduces a soil distortion factor (SDF) to establish a relationship between particle size compositions of soil and irradiance received by a tilted soiled solar panel. Particle size composition of five soil samples was determined using sieve analysis and artificial soiling experiments were performed to measure open circuit voltage (V-oc) and short circuit current (I-sh) to calculate power output of soiled panel. The power obtained from experimental data was compared with the ideal power output of a clean panel to quantify SDF at three regions of tilt angle. Further, SDF is expressed in terms of particle size composition of soil using regression analysis to calculate irradiance loss. It was observed that the irradiance loss varies with tilt angle and particle composition of soil. Soils rich in particles with 150 mu m diameter (Soil 1) and 300 mu m diameter (Soil 3) cause irradiance losses up to 6% and 21% while Soil 2 with high composition of 75 mu m particle size leads to maximum losses of 10%. Soil 4 with 300 mu m particles as its major composition causes losses as high as 22% in the same tilt angle range. Soil 5 having the highest composition of less than 75 mu m size particles causes 12% irradiance loss in 0-60 degrees tilt angle region.