Airwatt or air watt is a unit of measurement that represents the true suction power of vacuum cleaners.
It is calculated by multiplying the airflow (in cubic metres per second) by the suction pressure (in pascals).
is the air flow rate in cubic metres per second: Equivalently, in SI base units:
An alternative airwattage formula is from ASTM International (see document ASTM F558 - 13)[4] Where P is the power in airwatts, F is the rate per minute (denoted cu ft/min or CFM) and S is the suction capacity expressed as a pressure in units of inches of water.
Some manufacturers choose to use the fraction 1⁄8.5 rather than the ASTM decimal, leading to a less than 0.25% variation in their calculations.
So one then needs to analyse the curve created by both flow rate and waterlift as the opening changes from 0 to 2 inches (0 to 51 mm); somewhere along this line the power will attain its maximum.