A typical domestic model vacuum has a suction of about negative 20 kPa. This means that it can lower the pressure inside the hose from normal atmospheric pressure (about 100 kPa) by 20 kPa. The higher the suction rating, the more powerful the cleaner. One inch of water is equivalent to about 249 Pa; hence, the typical suction is 80 inches (2,000 mm) of water, = 2.88psi.
The power consumption of a cleaner, in Watts, is often the only figure stated. Many North American vacuum manufacturers only give the current in amperes (e.g. "12 amps") and the consumer is left to multiply that by the line voltage of 120 volts to get the power ratings in Watts. The power does not indicate the effectiveness of the cleaner, only how much electricity it consumes. The amount of this power that is converted into airflow at the end of the cleaning hose is sometimes stated, and is measured in air watts: the units are simply watts; "air" is used to clarify that this is output power, not input electrical power. This is calculated using the formula:
cleaning power (air watts) = airflow (CFM) × suction (inches of water) / 8.5
= airflow (m³/s) × suction (Pa)