Fan power calculator
Electrical input power from airflow, pressure and overall efficiency — plus the annual energy consumption, annual energy cost and Specific Fan Power (SFP) that follow from it.
How to use this calculator
- Enter the airflow and pressure.
- Enter the overall wire-to-air efficiency.
- Optional: add operating hours and electricity price.
- Read the electrical input power, annual energy consumption, annual cost and SFP.
What this calculates
The electrical input power a fan draws at a given duty point follows directly from the air power divided by how much of it survives the fan, transmission and motor:
P = Q × Δp / η
P = electrical input power, W
Q = airflow, m³/s
Δp = fan total pressure, Pa
η = overall (wire-to-air) efficiency -- fan × transmission × motor combined
η is the overall efficiency, not the fan (aerodynamic) efficiency alone. A fan quoted at 80% static efficiency but driven through an 85% V-belt and a 91% motor has an overall efficiency of roughly 0.80 × 0.85 × 0.91 ≈ 62% — that is the number this calculator needs, since it is what the electricity meter actually sees. Entering the fan's own efficiency alone will understate the real power draw.
Annual energy and cost
With the fan power known, the annual energy consumption and cost follow from how many hours a year the fan runs and the electricity price:
Annual energy = P × hours [kWh/yr]
Annual cost = Annual energy × price [currency/yr]
This is a constant-power estimate — the fan is assumed to run at this one duty point for the entered hours. A fan that spends most of its life throttled back on a VFD will use meaningfully less than this figure; use it as a worst-case / nameplate-duty screening number, not a substitute for a load-profile energy model.
Specific Fan Power (SFP)
SFP expresses the same electrical power per unit of airflow moved, which is exactly Δp / η — no separate calculation, just the same result read a different way:
SFP = P / Q = Δp / η [W / (m³/s)]
The badge above grades the result against the EN 13779:2007 SFP1–SFP6 scale (≤500, 500–750, 750–1250, 1250–2000, 2000–3000, >3000 W/(m³/s)), still the most commonly quoted quick reference for this metric. EN 16798-3:2017 superseded EN 13779 and sets its own SFP limits by system type (unidirectional/bidirectional) and airflow control (constant/variable), rather than one universal scale — check the applicable limit in your project's governing standard before using this as a compliance check; here it is shown as an indicative band only.