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Airwatt or air watt is a measurement unit of the effectiveness of vacuum cleaners which refers to airflow and the amount of power (watts) a vacuum cleaner produces and uses.[1][2] It can also be referred to as a measurement of the energy of the air flowing through an opening which is the same as the energy that electricity carries through the wire (watt).[3]

The airwatt is a useful measurement of vacuum cleaner motor efficiency, since the power carried by a fluid flow (in the case of a typical house vacuum the fluid is air) is equal to pressure times volumetric flow rate. The airwatt relates to actual airflow, while part of the electrical power (watts) consumed by a vacuum cleaner is dissipated into heat due to necessarily imperfect efficiency; two vacuum cleaners of the same airwattage have essentially the same suction, while devices of the same electrical wattage produce a difference in efficiency and may have substantially different airwattage."What is an airwatt?". 


The formula for airwatt differs between vacuum cleaner manufacturers.

The standard air watt formula is from ASTM International (see document ASTM F558 - 13)[4]

Airwatt = 0.117354 * F * S

Where F is the rate of air flow in CFM (Cubic Feet per Minute) and S is the suction capacity expressed as a pressure in units of inches of water. This makes one airwatt equal to 0.9983 watts.[5]

Below are some of the published formula of airwatts by different vacuum cleaner manufacturers

In terms of orifice plate

Air Watts = ( Vacuum suction (inches of water) x Air Flow (cubic feet/minute)/8.5 
Air Flow (CFM) = √13.35 X D^2/Vacuum suction

Where D is diameter of orifice holes[6]

In terms of litres per second (L/s).

1 L = 0.035315 ft<sup>3</sup> <ref></ref>
1/s = 60/min 
F = 60 × 0.035315 × <''airflow'' (L/sec)> = 2.1189 × <''airflow'' (L/sec)> 

In terms of kPa or mbar as vacuum cleaner suction measurement.

1 pressure in [[inches of water]] ≈ 2.49 mbar ⇒ 1 mbar = 1/2.49 inH2O
1 pressure in [[inches of water]] ≈ 249 Pa = 0.249 kPa ⇒ 1 kPa = 1/0.249 inH2O
S = 1/2.49 × ''suction'' (mbar)
  = 1/0.249 × ''suction'' (kPa)
cleaning power (air watts) = 0.117354 × [ 2.1189 × <airflow (L/s)> ] × [ 1/0.249 × <suction (kPa)> ]
cleaning power (air watts) 
                            ≈ 0.998 × <airflow (L/s)> × <suction (kPa)>
                            ≈ 0.0998 × <airflow (L/s)> × <suction (mbar)>

Alternative measurement formula[edit]

cleaning power (air watts) = airflow (CFM) × suction (inches of water) / 8.5

Vacuum cleaners[edit]

Hoover recommends 100 air watts for upright vacuum cleaners and 220 air watts for cylinder vacuum cleaners.[7]


  • ASTM Standard F558 Standard Test Method for Measuring Air Performance Characteristics of Vacuum Cleaners