A simple procedure has been developed for estimating the amount of the paddy pesticides used with each application method. We analyzed the usage for 14 insecticides used in Japanese paddy fields. Insecticide application was classified into five methods: ground application in paddy fields, nursery box application in paddy fields, aerial application in paddy fields, application in fields and orchards, and other applications. Based on the application method for each target pest provided in the pesticide application list, the fraction of usage with each application method was calculated, assuming that the usage was evenly distributed to each target pest. The usage with each application method in each prefecture was then calculated by multiplying the total usage by the fraction of usage for each application method. The accuracy of estimated usage in paddy fields was validated by a comparison with the estimated insecticide emission in paddy fields reported by the Pollutant Release and Transfer Register (PRTR) system. Estimation errors were largely around twofold; therefore, their accuracy would be similar. However, the errors became large when the usage amounts in paddy fields of each prefecture were small.