Most household appliances have a power label on the back or bottom. This label lists the maximum amount of power used by the equipment. To calculate the amount of power used, you must convert it to kilowatt hours, or kWh.
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Method 1 of 3: Calculating kWh from Equipment Label
Step 1. Look for the power information on the equipment label
Most high-power appliances have a power label on the back or on the bottom. Search this section for power information, which is denoted by the letter "W". This value is the maximum power the equipment uses when it is powered on, which may be much higher than the actual average power. The steps below will find a rough estimate of the number of kWh from this value. However, the actual kWh usage is usually lower.
Some appliances indicate a wattage range, such as "200–300W". It would probably be more accurate to choose the middle value of this range, or in this case 250W
Step 2. Multiply the number of watts by the number of hours of use each day
Watts measure power, or energy used over time. Multiplying it by the unit of time will give you the result in energy units, which is important for your electricity bill.
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Example:
A large 250 watt fan runs on average 5 hours per day. The daily power of the fan is equal to (250 watts) x (5 hours/day) = 1,250 Wh per day.
- For air conditioning and heating, make individual calculations for each season.
- The refrigerator only uses about of the time, or about 8 hours per day if you never unplug it.
Step 3. Divide the result by 1,000
One kilowatt equals 1,000 watts. This step converts your answer from watt hours (Wh) to kilowatt hours (kWh).
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Example:
You have calculated that your fan uses 1,250 Wh of power each day. (1,250 watt hours / day) (1,000 watts / 1 kilowatt) = 1.25 kWh per day.
Step 4. Multiply your answer by the number of days you counted
Now you know how many kilowatt hours (kWh) the equipment uses each day. To calculate kWH per month or per year, simply multiply by the number of days in the period.
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Example:
For a month (30 days), your fan will use (1.25 kWh/day) x (30 days/month) = 37.5 kWh per month.
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Example:
If your fan runs every day for a year, it will use (1.25 kWh/day) x (365 days/year) = 456, 25 kWh per year.
Step 5. Multiply by the electricity rate per kWh
Your electricity bill will list the price per kWh. Multiply this amount by the number of kWh to find the amount to be paid.
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Example:
If your electricity rate is IDR 2,000/kWh, turning on the fan will cost (2,000 / kWh) x (456, 25 kWh / year) = IDR 912,500 per year.
- Keep in mind that estimates based on the wattage listed are the maximum values. In reality, your bill will be less than this.
- If you want to find out the electricity tariff for a different class from the electricity tariff group in your home, you can search on the PLN website.
Method 2 of 3: Calculating kWh from Ampere and Voltage
Step 1. Find the amperage rating of your equipment
Some equipment labels do not list the wattage rating. In this case, find the amperage or "A" rating of the equipment.
Laptop and phone chargers may list two amperage values. Use the value labeled input
Step 2. Find the voltage in your area
In Indonesia, the standard electrical voltage for households is 220V. In Europe and in most other countries around the world, the voltage is between 220 and 240V.
Some large appliances such as washing machines may need to be connected to a dedicated 240V circuit. Check the voltage rating on the equipment label to find out. (The label only says the recommended voltage, but assume professionally assembled equipment will conform to these recommendations.)
Step 3. Multiply the amperage and voltage
Multiplying amperes and voltage will give you the answer in watts, or electric power.
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Example:
The label of the microwave is rated at 3.55 amperes and is plugged into a 220V power outlet. Means, the tool uses a power of 3.55 amperes x 220 volts 780 watts.
Step 4. Multiply by the hours of use per day
The power rating tells you the energy level used when the equipment is on. Multiply the rated power by the average number of hours the equipment is used per day.
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Example:
If the microwave is on for half an hour per day, multiply 780 watts x 0.5 hours/day = 390 watt hours per day.
Step 5. Divide by 1000
This division converts from watt hours (Wh) to kilowatt hours (kWh).
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Example:
390 watt hours / day 1,000 watts / kilowatt = 0.39 kWh per day.
Step 6. Multiply to find the number of kWh for the longer period
For example, if you want to find how many kWh your bill was for 31 days, multiply your answer by 31 days.
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Example:
0.39 kilowatt hour/day x 31 days = 12, 09 kWh.
Method 3 of 3: Using the Power Meter
Step 1. Purchase a power meter online
This device, also known as a watt meter or kilowatt meter, is used to measure the actual amount of power used by electrical equipment. This method is usually more accurate than using equipment label information.
If you are familiar with electrician's tools, you may be able to use a multimeter. This method requires access to the equipment's wiring harness while connected to the mains. Needless to say, don't disassemble anything unless you know what you're doing
Step 2. Connect the meter between the wall outlet and the appliance
Connect the power meter to a wall outlet. Connect the equipment to the power meter.
Step 3. Calculate kWh
Set the power meter to display kWh. As long as you continue to connect the power meter, it will calculate the number of kWh of the connected equipment.
- If your power meter only calculates in watts, you can use the method above to calculate kWh from this measurement.
- Follow the power meter's instructions if you're not sure how to change the settings.
Step 4. Use the equipment as usual
The longer you connect the power meter, the more accurate the measurement will be.
Step 5. Calculate your monthly or yearly kWh
The number of kWh displayed on the meter is the total amount when the equipment is connected to electricity. Multiply the value to calculate the number of kWh for a longer period of time.
For example, let's say the meter is on for 5 days, and you want to calculate the amount of power for 30 days. 30 divided by 5 equals 6. So multiply the kWh shown by 6
Tips
- If the label does not state the wattage, check the user manual. Many modern equipment labels will make your job easier, including the yellow EnergyGuide label in the US, and the blue and white label in the EU. Look for the kilowatt hour value listed as "kWh/year," "kWh/annum," or "kWh/60minutes." This is based on typical household use, which is often more accurate than the calculations above.
- There are appliances that have multiple power settings. The label may include individual information for each setting, or only the maximum value.
