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.
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?

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.