This study was conducted to determine the impact computational methods have on the mass of pesticide reported remaining in the fabrics. Each fabric specimen (10 × 10 cm) was marked along 5 × 5 and 8 × 8 cm lines. Pesticide stained with methylene violet dye was applied to the center of the fabrics with and without a water and oil repellent finish. Excess pesticide was removed after 10 min. The contaminated area was traced and calculated by using a) planimeter and b) maximum length and width of contaminated area (Lmax × Wmax). Prior to extraction, all specimens were cut into three pieces along the five and eight cm lines and each piece extracted separately. The amount of pesticide remaining in the fabrics was calculated using three different methods: a) mass per area (μg/cm2), b) mass per volume (μg/mL), and c) residual mass. Calculations for the first method, mass per area, were based on five different measures: a) contaminated area calculated by using planimeter, b) contaminated area calculated by using Lmax × Wmax, c) specimen area using 5 × 5 cm, d) specimen area using 8 × 8 cm, and e) specimen area using 10 × 10 cm. Findings of the study indicate that in unfinished fabrics, the difference in the mass per area measured by planimeter was as much as 2.2 times greater than that measured in 10 × 10 cm specimens. For fabrics with a water and oil repellent finish, differences were even more dramatic: the mass of pesticide per area reported using the planimeter method was up to 55 times higher than that of 8 × 8 cm specimens and 103 times higher than that of 10 × 10 cm specimens. Selection of appropriate computational method is very important to ensure accurate results and conclusion.