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Tips for converting watts into kWh
The watt (W), named after the Scottish engineer James Watt, measures the power of an electrical device. The kilowatt-hour (kWh), on the other hand, measures the energy consumption of that same device over one hour. These two units are extremely useful for better understanding your energy consumption and choosing your electronic devices and household appliances. So how do you convert watts into kWh? Follow the guide!
Watts, kilowatts and kilowatt-hours: what’s the difference?
First, it’s essential to understand the distinction between watt and kilowatt-hour, and how they are used!
Watt (W) and kilowatt (kW): the reference unit for measuring power
Just like the meter measures length, the liter measures volume, and the gram measures mass, the watt (W) is the unit used to measure the power of an electrical device. With watts, you can determine the electrical power of each appliance.
For example:
an incandescent bulb has a power of 40 W
a microwave oven is around 900 W
The wattage of appliances is displayed on their packaging. The same applies to its multiples, such as kilowatts (kW) and megawatts (MW). Here are the equivalences:
1 kilowatt (kW) = 1000 watts (W)
1 megawatt (MW) = 1000 kilowatts (kW)
- 1 gigawatt (GW) = 1000 megawatts (MW)
Conversion table: from watt (W) to gigawatt (GW)
Gigawatt (GW) |
Megawatt (MW) |
Kilowatt (kW) |
Watt (W) |
1 |
1000 |
||
1 |
1000 |
||
1 |
1000 |
How do you calculate the power of a device in watts?
Unlike meters, grams, or liters, watts cannot be measured directly without calculation. The formula is:
P (power in watts) = U (voltage in volts) × I (current in amperes)
The kilowatt-hour (kWh) to measure energy consumption
The watt-hour (Wh) is used to measure the energy consumption of an electrical device. In other words, it represents the energy consumed by a 1 kilowatt (or 1000 watts) device running for one hour. It is therefore a unit of energy.
Two factors are involved:
duration (number of hours or days the device is in use)
device power
Like the watt, the watt-hour (Wh) has multiples: kilowatt-hour (kWh), megawatt-hour (MWh), and gigawatt-hour (GWh).
Conversion table: from watt-hour (Wh) to gigawatt-hour (GWh)
Gigawatt-hours (GWh) |
Megawatt-hours (MWh) |
Kilowatt-hours (kWh) |
Watt-hours (Wh) |
1 |
1000 |
||
1 |
1000 |
||
1 |
1000 |
Converter: how to switch from watts to kWh
The formula to convert watts into kWh is:
consumption (in kWh) = number of hours × number of days × power / 1000
For example:
a 3000 W oven used for 1 hour consumes 3 kWh (i.e. 3000 Wh) and 1,125 kWh per year when used one hour per day, 7 days a week
a 900 W vacuum cleaner used for 1 hour per week consumes 46.8 kWh per year
This calculation allows you to estimate the energy consumption of your appliance (expressed in kWh) based on its power.
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kVA to understand your electricity consumption and needs
What is kVA (kilovolt-ampere)? This unit is used in France to indicate the maximum power capacity of your electrical installation (your meter). When choosing your energy contract, you subscribe to a specific maximum power level depending on your needs and appliances.
How to choose the power of your electricity meter
The power of your electricity meter depends on the size of your home, the appliances you use, and your heating system. In France, this power is expressed in kVA (not in W or kWh), as shown on your energy bills.
It is important to accurately estimate your electricity needs. Otherwise, you may experience frequent circuit breaker trips or pay unnecessarily high bills compared to your actual consumption.
Good news: you can increase or decrease your meter power at any time and remotely if you have a smart Linky meter.
The formula to convert kW into kVA is:
1 volt = 1 watt / 1 ampere and 1 kVA = 5 amperes
What is the typical power level of a home in France?
Generally, a 2- or 3-room home requires a meter with a power level of 6 kVA. Most French homes have a meter power between 6 kVA and 9 kVA.
- Also read: our guide to choosing your electrical power
Kilowatt-hour, kVA or watt: use them to understand your consumption
kVA is used to estimate the required power capacity of your electricity meter and determine your electricity plan.
Watt (W) and kilowatt (kW) are units that indicate the power of your appliances — in other words, the energy they use to operate.
The kWh (kilowatt-hour) measures the energy consumption of an electrical device over one hour.
You can easily calculate the annual electricity consumption in kWh of your appliances if you know their power.
These calculations and conversion methods help you estimate your energy bill and switch offers if your electricity needs change over time.
What is a watt?
The watt is a unit used to measure power. To find out the power of an appliance, you can check its packaging, where a number is displayed alongside the symbol W.
For example: the average power of a 50-liter fridge is 100 W.
What is a kilowatt-hour?
The kilowatt-hour is a unit of energy used to estimate the consumption of an appliance based on its power over one hour.
Why is it important to estimate your electricity consumption accurately?
Estimating your consumption is essential to choosing the right electricity meter power for your needs. If the selected power is too low, your circuit breaker may trip frequently. If it is too high, your bills may be unnecessarily expensive compared to your actual usage. Keep this in mind!
