In infusion therapy, flow rate errors are caused by changes in the droplet volume dripped from drip chamber. The purpose of this study is to determine the change in droplet volume when surface tension, viscosity, density, and flow rate are varied. The droplet mass in a continuous drip is precisely measured and the droplet volume and standard deviation are determined for each 100 drops. At drip nozzle A, the rate of change in droplet volume was -44.78% at the change in surface tension, -12.14% at the change in viscosity, -5.70% at the change in density, and 8.14% at the change in flow rate. The volume change rate when double the surface tension, viscosity, and density were changed was 43.18% at the change in surface tension, -2.87% at the change in viscosity, and -16.10% at the change in density. The volume change rate affected by the viscosity change was slight. An experimental equation was tried to calculate the droplet volume of each condition. Since a change in surface tension causes a significant change in droplet volume, infusion therapy used drugs with significantly different surface tensions needs to pay attention to flow rate errors. It is recommended that the surface tension of drugs used for infusion is written on the package insert.