Also called: duct pressure loss calculator · air pressure drop calculator · HVAC static pressure calculator · fan ΔP calculator.
Calculate air pressure loss in HVAC ducts, fans, and industrial extraction systems. Free online tool for oil-mist collection, dust extraction, and standard HVAC — no signup, no installation. Built on Darcy–Weisbach friction + Idelchik / ASHRAE K-factors with application-specific correction for oil mist and dust.
Optional 3-minute walkthrough of the calculator and its inputs.
1. Air properties (standard conditions, 20°C / sea level): ρ = 1.2 kg/m³, μ = 1.81×10⁻⁵ Pa·s.
2. Section flow properties (per section): D = section diameter (m), A = π·D²/4, V = Q/A, Re = ρ·V·D/μ.
3. Friction factor (Swamee–Jain, explicit): f = 0.25 / [log₁₀(ε/3.7D + 5.74/Re⁰·⁹)]². ε from material: galvanized = 0.15 mm, aluminum = 0.0015 mm, black steel = 0.045 mm.
4. Straight-tube friction (Darcy–Weisbach): ΔP_f = f·(L/D)·½·ρ·V² per row.
5. Fitting loss (K-factor, Idelchik / ASHRAE averages): ΔP_m = K·½·ρ·V² per row. K values: 90° elbow = 0.18, 45° elbow = 0.20, T-junction = 1.20, Y-connector = 0.60, reducer = 0.10.
6. Reducer step-down: When a row is a reducer, the section's effective diameter is updated to the reducer's outlet for all subsequent rows.
7. Application correction (K_app): Total raw loss is multiplied by 1.0 (HVAC), 1.15 (oil mist, accounts for liquid film drag), or 1.25 (dust, accounts for particle acceleration and wall impact).
8. Final result: ΔP_total = (Σ ΔP_f + Σ ΔP_m) × K_app. Recommended fan static pressure = ΔP_total × 2 (industry 2× safety margin).
Single-run pressure drop only, no multi-branch balancing, no fan matching, no temperature/altitude correction. K-factors assume turbulent flow (Re > 4000). Adjust per-component K-values in the library if your installation deviates from ASHRAE defaults.
Air pressure loss (also called air pressure drop or duct pressure loss) is the reduction in static pressure as air flows through a duct, fitting, filter, or other component. It is measured in pascals (Pa) and is the single most important factor when sizing a fan or extractor for an HVAC, oil-mist, or dust-collection system. Pressure loss comes from two sources: friction along straight duct walls and minor (fitting) losses at elbows, branches, transitions, and filters.
Air pressure loss is the sum of friction loss in straight ducts (Darcy–Weisbach, calculated with the Swamee–Jain friction factor) plus the K-factor losses of every fitting in the run (90° elbow K ≈ 0.18, 45° elbow K ≈ 0.20, T-junction K ≈ 1.20, Y-connector K ≈ 0.60, reducer K ≈ 0.10). For oil-mist extraction multiply the total by 1.15, for dust collection multiply by 1.25, then double the result for fan safety margin. This calculator does all of the above automatically — enter airflow, pick your material and application, add the duct sections, click Calculate.
There is no physical difference — both terms describe the same quantity (static-pressure reduction, in Pa). “Pressure drop” is the engineering / ASHRAE term; “pressure loss” is the phrasing used by HVAC installers, ductwork suppliers, and most European industrial catalogues. Search engines and supplier documentation mix the two freely; this calculator handles both, and the methodology treats them as identical.
For a typical galvanized HVAC supply duct at 1,500 m³/h, expect roughly 1 Pa per metre of straight duct (200 mm diameter, f ≈ 0.02) plus 5-12 Pa per 90° elbow and 30-70 Pa per T-branch. ASHRAE recommends a target friction rate of 0.8-1.2 Pa/m for low-pressure mains. For industrial oil-mist and dust extraction, total static pressure is usually 800-2,500 Pa once filter and cyclone losses are added — the calculator gives you the duct-only figure; add filter loss separately.
It depends on the elbow geometry. Common ASHRAE / Idelchik values: die-stamped 90° elbow (r/D = 1.5) → K = 0.18; mitered 90° without vanes → K = 1.3; mitered 90° with single vane → K = 0.5; smooth-radius 90° (r/D = 1.0) → K = 0.23. This calculator uses the die-stamped r/D = 1.5 value of 0.18, which is the most common HVAC fitting; adjust the K in the methodology section above if your installation uses a different geometry.
Two numbers: airflow (m³/h) and static pressure (Pa). The airflow is set by the application — for oil-mist, 1,500-2,500 m³/h per CNC; for dust, 2,000-5,000 m³/h per cell. The static pressure is the duct pressure loss from this calculator, plus filter and cyclone loss (typically 500-1,500 Pa for an oil-mist filter cartridge). Industry practice adds a 2× safety margin on top — this calculator already applies that, so the “Fan (2× safety)” output is your minimum fan rating.
