Abstract: A method of determining a characteristic of a fluid involves measuring a sonic transit time (102), along a non-perpendicular path, through the fluid. The sonic transit time is used to determine a speed of sound in the fluid (104). A measured flow rate (106) is determined from the sonic transit time. A friction factor (108) is calculated using the speed of sound and the measured flow rate. Next, a velocity profile (110) is determined using the friction factor. Finally, an adjusted flow rate is calculated (112) using the velocity profile.