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How can you tell or measure how many watts a resistor can handle.?


Let's say I salvage a few resistors from an old electronic, how can I tell if it's a 1/8 watt or 1/4 watt etc?
I have a multimeter if need be.

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If smoke comes out, then that means you have exceeded the power rating. ;-)

Seriously though, it's like the other answerers have been saying.  Physically larger (in length, width, and height)  resistors dissipate more power.

I took a snapshot for you, of a bunch of typical 1/8, 1/4, 1/2, 1, etc resistors, and I think I've even got the power ratings labeled right.  If I don't, I'm sure some considerate person (or robot) will post a reply explaining how it's 'sposed to be.
resistors_by_power_rating.jpg
surlistyc (author)  Jack A Lopez6 years ago
If I had a few more ounces of whiskey in me, I could hug you!
Thanks for taking the time to set up this snapshot man! it gives me hope. Hope for a better internet. Hope that one day we can banish the troll mongers. Hope that I might be able to save the universe from an impending deathstar.

Seeing as you are so fancy (Not being sarcastic) Maybe you can help answer my other question? https://www.instructables.com/answers/how-do-you-figure-out-what-resistor-to-use-for-a-5-6/

Steveastrouk helped me so much, so that I don't know what he's talking about, maybe you can dumb some things down for me?
orksecurity6 years ago
Size really is the simplest answer; they're pretty standardized. If in doubt, use the larger one or buy one that has the rating you need.
Re-design6 years ago
They are different sizes.

surlistyc (author)  Re-design6 years ago
That's the only way to tell?
At the risk of sounding stupid:
I bought an assorted pack the other week (of 100) and now I don't remember how many watts they were. So I have to go to the store with a resistor and compare sizes? If so that's not a problem, I was just wondering if there might be another way.

Thanks Re-design.
.  In most cases, physical size is a pretty good indicator of watt rating. Find the datasheets for a few representative resistors of various wattages and get the measurements (or go to the store as you mentioned with a caliper). Compare measurements to what you have. When in doubt, use the lower value.