Pitot Traverse Airflow from Point Readings (Velocity-Averaged)

ScopeConvert EACH equal-area point's velocity pressure to a velocity (V = 4005 x sqrt(VP)) and average the velocities, because velocity is what integrates to flow -- not the velocity pressures. Averaging the VPs first and taking one square root always reads high, since sqrt is concave. Four readings 0.09/0.16/0.25/0.16 in wc in a 24x12 duct give 1,602 fpm and 3,204 CFM velocity-averaged, where the single-average-VP shortcut reads 3,254 CFM, 1.55 percent high. Space the points on an equal-area or log-Tchebycheff traverse per NEBB/AABC/ASHRAE. A field measurement, not a substitute for a calibrated flow station.

Formula or tableV_i = 4005 sqrt(VP_i) at each equal-area point; V_avg = mean(V_i); A = (w x h)/144; CFM = V_avg x A. The single-average-VP shortcut V = 4005 sqrt(mean VP) reads high because sqrt is concave.

Source and editionPitot-traverse airflow averaged per ASHRAE Fundamentals / AABC / NEBB field practice: average the point velocities, not the velocity pressures. By name.

Free accessThe V = 4005 sqrt(VP) standard-air relation and the average-the-velocities traverse method are standard published air-balancing procedures.

What governsEstimate. AHJ and licensed professional govern.

API field namesvp_readings, w_in, h_in, v_avg_fpm, area_ft2, cfm, v_vp_average_fpm, overread_pct, point_count

• Air density optional (added 2026-10-09): V = 4005 sqrt(VP x 0.075/rho), the standard-air constant scaled for the entered density (the exact form is 1096.2 sqrt(VP/rho)); 0.075 lb/ft^3 leaves it unchangedASHRAE Fundamentals; air-density-correction
• Velocity from VP V = 4005 sqrt(VP) for standard air, per pointASHRAE Fundamentals
• Correct average average the point velocities, not the velocity pressuresAABC / NEBB field practice
• Standard air 0.075 lb/ft^3 unless an air density is entered; air-density-correction gives the density at altitude or high temperaturescope of this tile