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Should i buy Watt Meter (aka killawatt) or regular Clamp on meter to determine the device wattage?

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As the title says i need to know what should i buy? which one would give me the most accurate reading? I want to know how much power my appliances consumes, tv, washing machine etc....

Also i need to buy a new ups for my PC so just wants to know how much power my pc eats. I have a 500W power supply, but that doesn't mean my pc uses 500w all the time.

My last ups was 1100VA or 1 KVA, i think the shopkeeper fooled me into buying this one as i had no prior knowledge about power consumption at that time.

My old ups although is working ok but it's batteries are dead, new ones would cost around 70 bucks, it takes two 12v 7ah batteries in series..

I was thinking instead of buying new batteries i could buy a new ups instead, one that is efficient for my PC's power consumption. I just need 10 to 15 minutes of backup.

So it all comes down to the title itself. Which device should i buy to know the average consumption of my pc? killawatt is a little expensive while clamp meter is cheap.

Let me know your thoughts.


Active Member
Get the killawatt. It gives you a lot of info that a clamp meter doesn't, it costs less, and you don't have to hack into your device cords to clamp around a single conductor.

Daniel Wood

I would recommend a killawatt style device if you want to measure the consumption of a single device. I used an Efergy plug in monitor (don't think its on sale anymore), and that gave me both average and instantaneous usage, as well as power factor correction and other useful bits of information.

You can measure your instantaneous household consumption for free (like a meter clamp) by counting how fast the LED blinks on your power meter.
If your led blinks fast enough, you can use a BPM counting tool like http://all8.com/tools/bpm/, and then match the flashes coming from your meter.

Then you convert using to Watts by using: BMP*60 = W
example: 12bpm * 60 = 720W

You may have to subtract your household background consumption first if you want to measure your PC usage

schmitt trigger

Well-Known Member
Clamp meter will essentially measure currents. Some higher end models, have additional functions, but they won't measure true power.
Don't get me wrong, the clamp meter is an extremely useful instrument that no serious electrician should do without. But for your needs, you do require a power meter.


Well-Known Member
Most Helpful Member
The only thing I dont like about my Killawatt is that if I leave it plugged in anywhere in the house, I can find its RFI harmonics on my ham HF receiver. Otherwise, it is a very useful device to let you learn what is running up your electric bill...
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