# How convert kWh to W

I want to know if there is an approximate or exact way to know the consumption in watts of household appliances in a house from the monthly consumption that reaches the bill.

Taking into account that it arrives in kWh and I want to convert any value, which would be the best option.

305 kWh to W

• Not if you don't know exactly how much time each device is powered on. But most devices list the wattage on the back... – Trevor_G Feb 15 '18 at 15:09
• Do these appliances have a name plate, or something similar? Usually the wattage will be listed there. – Tyler Feb 15 '18 at 15:11
• Divide by hours. – Brian Drummond Feb 15 '18 at 15:14
• You can't do what you want. Watts are units of power. Watt hours are units of energy. You can't convert from one to the other. If you have watt hours and know how much time the device was operating then you could calculate the average power. – JRE Feb 15 '18 at 15:16
• If you operate a light bulb with 100 W for 24 hours and 31 days, the monthly consumption is 100 * 24 * 31 = 74,400 Wh = 74.4 kWh. If you use the same bulb only 2 hours each day, you use 100 * 2 * 31 = 6.2 kWh. – Uwe Feb 15 '18 at 15:17

If something uses N kWh in a 30-day month, has an average consumption of

$$N \frac{1000\text{ W/kW}}{720\text{ h/month}}\text{ watts}$$

In other words, to convert "energy" to "power", divide by "time".

Just as an example, suppose you use a 1500 W toaster for 3 minutes to make toast for breakfast. That would be a total of

$$1500\text{ W}\frac{3\text{ min}}{60\text{ min/hr}} = 75\text{ Wh} = 0.075\text{ kWh}$$

of energy. If you do that every day for a month, the total energy would be

$$0.075 \cdot 30 = 2.25\text{ kWh}$$

The average power of the toaster over the entire month would be just

$$2.25\text{ kWh} \frac{1000\text{ W/kW}}{720\text{ h/month}} = 3.125\text{ watts}$$

as compared to its peak power of 1500 watts.

In other words, a 3-watt alarm clock, which runs continuously, costs you the same amount in electricity as the toaster.

• 1- (305KWh * 1000W/KW)/(720h/month) 2 - 305000W/(720h/month) 3 - 423.61W/(h/month) – Pedro Miguel Pimienta Morales Feb 15 '18 at 15:22
• Grace, but seeing the answer, the best way to know exactly, is to investigate every electronic device that is in a house to know. How reliable can these be?. options – Pedro Miguel Pimienta Morales Feb 15 '18 at 16:31
• @Pedro, your question asks how to find the total power used by your house. You can get the total energy for the month from your bill. Use the equation in Dave's answer and you get the average power used by your house over the month. If this isn't the answer you want, you should edit your question to clarify what you're asking. – The Photon Feb 15 '18 at 17:39
• Also, I don't know where you live, but in my area a couple years ago they replaced all the electric meters with "smart" meters that will show you the "instantaneous" power used every minute or so. If you have one of those meters, just go look at the display on the front of it and wait for it to cycle around to the power reading. – The Photon Feb 15 '18 at 17:40
• @ThePhoton i live in colombian, the company don't use this "smart" things, thanks, is use full – Pedro Miguel Pimienta Morales Feb 15 '18 at 19:40

If energy consumption in one month is 305kWh the mean (i.e. average) power consumption during that month is $\frac{305kWh}{30 \times 24h}=\frac{305000}{720}W\approx 423W$ (assuming a 30 day month).

• i.e close to 425W average – Trevor_G Feb 15 '18 at 15:15
• @Trevor_G: yes, but also close to 135$\pi$W ;-) – Curd Feb 15 '18 at 15:20
• @Pedro Miguel Pimienta Morales: as I wrote: it is the mean power during that whole month. E.g. if you operate one 423W load for a whole month it would consume 305kWh. – Curd Feb 15 '18 at 15:20
• Or 423Wh per hour – Christian Feb 15 '18 at 15:30
• @Christian: or 423J per second. – Curd Feb 15 '18 at 15:42

All incorrect. The best you are getting is AVERAGE power use.

If I use 1kW per hour every day for 30 days, I get 30kWh. However if I use 30kW for 1 hour per day, but only 1 day per month, or 15kW for 2 hours per month, or 2 kWh per day for 15 days, I ALSO get 30kWh. So knowing that I used 30kWh in a month CANNOT tell me how much power I used on any given day, hour, minute or second.

• "1kW per hour" is non-sensical as the kW is power measurement and is an instantaneous value. If you mean 1 kWh per hour for 30 days then your calculation should be 1 kWh x 24 x 30 so you are out by a factor of 24. "All incorrect." It is not clear whether this is aimed at the OP or the other answer. -1 – Transistor Feb 16 '18 at 10:43