Hydraulic Hose Sizing Flow speeds at the lower end of the ranges should be used when designing for a continuous duty system. The inside diameter of the hoses should be chosen such that the needed flow rates can be supplied at fluid speeds within the acceptable ranges listed above. The following equation can be used to relate flow desired flow rate to hose diameter: Where Q is fluid flow rate in gallons per minute, D is the inside diameter of the hose in inches and V is fluid speed in feet per second.