Airflow Volume Calculator
Volumetric airflow (air quantity) Q is the product of air velocity and the cross-sectional area it passes through: Q = velocity x area.
Enter Values
Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Enter the airway (drive/drift) width and height in metres for a rectangular cross-section.
- Enter the average air velocity in metres per second (m/s), e.g. from an anemometer traverse.
- Read the airflow quantity Q in m3/s and m3/min, plus the cross-sectional area used.
How it works
Volumetric airflow (air quantity) Q is the product of air velocity and the cross-sectional area it passes through: Q = velocity x area. For a rectangular airway the area is simply width x height. With velocity in m/s and area in m2, Q comes out in m3/s; multiplying by 60 gives m3/min, the unit often quoted in mine ventilation reports.
The velocity used should be the average (mean) velocity over the whole cross-section - a single centre-line reading over-reads because air is slower near the walls, so a proper anemometer traverse or a wall-correction factor is normally applied. This tool assumes a clean rectangular section of constant area and does not account for arched backs, obstructions, leakage, air density or friction losses. It is a first-pass estimate only; final ventilation design must be signed off by a competent ventilation engineer.
Worked example
Airflow in a 5 m x 5.5 m intake drive at 1.2 m/s. A rectangular intake drive is 5 m wide and 5.5 m high, with an average air velocity of 1.2 m/s. The cross-sectional area is A = 5 x 5.5 = 27.5 m2. The airflow quantity is Q = velocity x area = 1.2 x 27.5 = 33 m3/s, which is 33 x 60 = 1,980 m3/min. This is the volumetric air quantity passing that section each second.
Common mistakes
- Using a single centre-line velocity reading as the average - it over-estimates Q because air moves slower near the ribs and back; use a traverse or correction factor.
- Mixing units: entering velocity in m/min or ft/min while width and height are in metres. Keep velocity in m/s to get Q in m3/s.
- Treating an arched or irregular airway as a full rectangle - the true area is smaller than width x height, so this over-estimates airflow.
Frequently asked questions
What is the difference between m3/s and m3/min?
They are the same airflow expressed over different time bases: 1 m3/s = 60 m3/min. Mine ventilation quantities are often quoted in m3/s for engineering and m3/min in day-to-day reporting. This tool shows both.
Do I need the average velocity or the maximum?
The average (mean) velocity across the whole cross-section. Air is slower near the walls and back, so the centre-line reading is higher than the average. A proper anemometer traverse or a wall-correction factor gives the mean velocity Q is based on.
Does this account for air density, leakage or friction?
No. This is a pure Q = velocity x area calculation for a clean rectangular section. Air density, standardisation to a reference density, duct/airway leakage, friction (pressure) losses and obstructions are separate steps in a full ventilation design and should be handled by a competent ventilation engineer.
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