When choosing an electric vacuum cleaner, power plays an important role. Prospective vacuum-buyers will almost always look at the wattage of an appliance. However, the electrical power of a vacuum cleaner is not an indication of its suction power and cleaning ability.
What really matters is the combination of the maximum air flow (measured in litres per minute) and the maximum negative pressure (in mbar). The air flow must be fast enough so that it can transport the dirt from the nozzle to the container. Nowadays, suction power is usually measured in air watts (AW). This denotes the amount of energy produced by a given amount of air flowing through an opening.