What is a wattmeter and how does it work? These are the questions we will answer for you today. So keep reading and find out everything you need to know about how a watt-meter can help you find out how much electricity you and your appliances use.

A wattmeter or power meter is an instrument with which electric power is measured in watts (W). Watts are a result from the product of current and voltage. This means that the watt meter simply measures how much electricity has been used under a certain time. This number is then recalculated and the wattage meter shows you how much power would have been used if the device had been running for a full hour. So if the display reads 1000W that means the device consume 1000W per hour, or in other words 1 kilowatt hour or 1 kWh

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The term Wattmeter is mainly used for the classical electro dynamic instruments with which the active power is measured in low voltage networks such as a home. At higher frequencies we speak of power meters. But often you will find household wattmeters to be incorrectly labeled as power metes in the electronic stores.

The electricity meter you already use in your home is actually nothing else then a big wattmeter. Another typical one is that small digital device that you would plug in between a household appliance and the mains in the wall. The watt meter will then show you how much power that particular appliance is consuming.


How a wattmeter works

A wattmeter does its measuring with the help of a coil pair. One coil works as the power coil and the other serves as a voltage coil. The two coils are arranged in relation to one another in right angles and one of the coils is also movable. The fixed is the current coil, the rotatable tension coil. When electricity flows through the watt meter it will create magnetic fields inside the coils. As we all know magnets ether attract or repel each other, thus forcing one of the coils to move. When that happens a reading can be made depending on how great the movement of the coils are. In the olden days the analog wattmeter’s used a needle attached to the coils that would move in synchronism with it showing us the wattage on a scale. Now we will use digital technology instead. Digital wattmeters work with A / D converters that digitize the instantaneous values of current and voltage, and a microprocessor to calculate the different power values.

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Wattmeters don’t work for small currents

Wattmeters have switchable measuring ranges and can detect powers of a few milliwatts (mW) up to a few kilowatts (kW). The range measured can be changed with a neat trick. Quite simply one could choose not to use the whole coil, a smaller coil would mean a smaller electric field and this in turn would heighten the sensitivity of the watt meter.

But even though the common wattmeter’s measuring range is somewhat changeable trying to detect very small currents is still a problem. For this task a more expensive low current meter should be used. The limit for possible accurate readings done by a cheap watt meter is 10 watt. If you have a device that consumes lower than that, a special meter needs to be purchased. This is why trying to measure how much electricity a device uses when it is in standby could be a problem. Say you try to measure your TV in standby mode witch consumes 3W. Unfortunately the watt-meter will spew out any number between 0 to as high as 15,15W. The readings done for such a small current are doomed to be totally useless

To get around this problem another known power consumer would have to be attached to heighten the values and get the power consumption above the magic line of 10W. If you for example would have added a 20W light bulb to the above example the wattmeter would have shown you a value of ca 23 W, after subtracting the 20W the accurate wattage for the TVs standby mode would have been revealed.


Tips for using the watt meter

A good way to use a watt meter is to see if your household appliances consume power even if they are set to “off”, for example your radio, television, computer, game console, etc. If you find that they unnecessarily do consume electricity a good idea would be to connect them to a multiple plug equipped with switch. This makes it easy to disable it completely without having to remove the plug out of its socket. But remember to get a correct value for such a small current the above method with an extra light bulb need to be utilized.

For appliances with variable electricity consumption for example a fridge or a freezer a wattmeter could be set to measure the device during 24h and then the meter would output an average value in kWh for you.



A wattmeter can really help you to locate not only the secret power consumers, but also the major power hogs in your home. This will help you find strategies to lower your power consumption and to make educated choices on weather or not you want to exchange the power hungry appliances themselves. A watt meter is a small investment compared to the benefits one gets from knowing where the power is consumed.

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