The performance of a vacuum cleaner can be measured by several parameters:

• airflow, in cubic feet per minute (CFM or ft³/min) or litres per second (l/s)
  
• air speed, in miles per hour (mph) or metres per second (m/s)
  
• suction, vacuum, or water lift, in inches of water or pascals (Pa)

The suction is the maximum pressure difference that the pump can create. For example, a typical domestic model 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.

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"[1]) 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:

Air watts measured at the vacuum's motor can differ by as much as 50% (depending on the type of vacuum) from the air watts measured at the end of the hose. This is most noted in Central Vacuums.

Some smaller vacuum cleaners are light-weight, portable, and rechargeable, instead of using AC power.