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    Velocity Traverse Worksheet

    Mobile
    Measurement positions
    Round duct — traverse positions by size

    Two planes 90° apart. Distance from duct wall = point factor × diameter (in.).

    Duct sizePointsPoint factors (× diameter)
    4" – 8"12 total (6 per plane)0.043, 0.146, 0.296, 0.704, 0.854, 0.957
    8" – 12"16 total (8 per plane)0.032, 0.105, 0.194, 0.323, 0.677, 0.806, 0.895, 0.968
    12" – 18"20 total (10 per plane)0.024, 0.082, 0.146, 0.226, 0.342, 0.658, 0.774, 0.854, 0.918, 0.976
    18" – 24"20 total (10 per plane)Same as 12"–18"
    24" – 36"20 total (10 per plane)Same as 12"–18"
    36" – 48"20 total (10 per plane)Same as 12"–18"
    48" – 72"20 total (10 per plane)Same as 12"–18"
    Pitot tube
    Pitot tube — measurement process & accuracy
    • How it works: The tube has two ports — one faces the airstream (total pressure), one is perpendicular (static). Your meter reads velocity pressure (VP) = total − static. Velocity = 1096 × √(VP ÷ density factor).
    • Placement: Use a straight duct run — at least 5–10 diameters downstream and 2–3 diameters upstream from elbows, dampers, or equipment. Center the probe in the duct at each traverse point.
    • Alignment: Point the tip directly into the flow. Keep yaw and pitch within about ±5° of parallel to the duct axis; misalignment reduces the reading and understates velocity.
    • Traverse: Use the number of points and positions from the “Measurement positions” guide for your duct size. Take readings at each point; average for mean velocity.
    • Accuracy: Enter correct barometric pressure and air temperature so density (and velocity) are right. Ensure tubing is sealed and the meter is zeroed. In turbulent or swirling flow, allow the reading to stabilize before recording.
    Notes
    Notes:
    • Blue/required fields need input. Velocity and flow are calculated from your entries.
    • Duct size in inches: circular = inside diameter; rectangular = inside L and W.
    • Barometric pressure: standard sea level = 29.92 inHg.
    • Velocity = 1096 × √(VP / density factor). Density = (1.325 × baro) / (temp °F + 459.69).
    • Open from email: Put a link to this page (e.g. https://yourserver.com/velocity-report.html) in your email; when recipients click it, it opens in their default browser.

    Project information

    Velocity pressure (in. w.g.) — 10 points × 5 positions

    Enter velocity pressure for each traverse point. Cell color shows velocity vs design (blue = below, green = at design, red = above).

    Pt
    1
    2
    3
    4
    5
    1
    2
    3
    4
    5
    6
    7
    8
    9
    10
    < 70% design 70–90% At design 100–120% > 120%

    Velocity report

    Free area
    —ft²
    Density factor
    —
    Design velocity
    —FPM
    Actual velocity (avg)
    —FPM
    Actual flow
    —ACFM
    % of design
    —%

    Duct & conditions