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What is the difference between a 1206, 0805 and a 0603 SMD resistor, as far I know they all have a resistance of 10.7K?

I going to need one for my little 5v DC buck converter.

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    \$\begingroup\$ Size. And voltage rating. \$\endgroup\$ – Ignacio Vazquez-Abrams May 21 '18 at 22:52
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    \$\begingroup\$ Actually, all of them don't have a resistance of 10k7. A very small percentage of them do. \$\endgroup\$ – Wesley Lee May 22 '18 at 3:26
  • \$\begingroup\$ @WesleyLee Thank you, for your answer. Didn't know they were size codes, before now. Thanks for clearing it up. \$\endgroup\$ – Artonn May 22 '18 at 14:00
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The codes you are referring to are size codes, e.g. 1206 means 0.125x0.060 inches.

There are some other differences, except for size.

Smaller resistors probably feature a lower power and voltage rating, but can have smaller parasitic components, ESL and parallel capacitance. I would not expect the parasitics to be an issue, just be sure to get one with the required power rating.

If you need to hand solder them, I suggest not going too small,e specially if you do not have any experience. 0603 should be fine for almost everyone, 0805 even more so, 1206 is a huge beast you can solder with your hands tied and your eyes closed.

As usual, if you have doubts always refer to the manufacturer datasheet.

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  • \$\begingroup\$ Thank you very much for your explanation, I'm very new to this but I find it very interesting. I'll go with the 0603 as I believe they're close to the size used on this one: i.imgur.com/lu5EzTr.png \$\endgroup\$ – Artonn May 22 '18 at 13:56
  • \$\begingroup\$ those look more like 0805 or 1008 actually \$\endgroup\$ – Vladimir Cravero May 23 '18 at 6:57
  • \$\begingroup\$ I found my digital ruler and measured them now, they're 0805 and 1206 sized. Now I just need to identify that damn chip. \$\endgroup\$ – Artonn May 23 '18 at 16:36
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They are different sizes.

1206 means 0.12 inches by 0.06 inches (3.2 x 1.6 mm). 0603 means 0.06 by 0.03 inches (1.6 by 0.8 mm). And so on. (Wikipedia)

The smaller ones will most likely have lower power and voltage ratings, because they are smaller.

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Here are the relative SMT sizes:

enter image description here Source: groups.io

Usually size also corresponds to power rating (the more surface area and pin area the part has, the more heat it can dissipate and the larger amount of power it can handle.

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