I need some resistors (470 ohm, 3kohm) for a project, i have no idea how much current will pass through them, on digikey, most of them have 0.25W, but a few get up to to 2W, should i go with 2W since it’s the highest? (That way they won’t melt, just in case?)
so look at the LED resistors first, 5v supply, a red LED drops about 2v, so the resistor will have about 3v across it. 3v / 470Ω ~= 6mA 6mA * 3v = ~.02W
the disadvantage is higher wattage resistors are much larger, and you don't gain any real advantage. most "arduino type" projects are fine with 1/8W or higher resistors
when you are going to be passing 0.005-0.018w through the resistors, an 0.125w resistor is still "5x safety over-built" and an 0.25 exceeds pretty much every safety standard I've ever seen at ~12x over-built safety factor. I don't see any benefit to using 0.5w resistors here, but I guess as long as they're all thin-film or carbon-type and NOT wire-wound, you'll probably be fine.
when a "digital signal" goes from LOW to HIGH (or vice versa) the voltage and current change rapidly, which is "AC" as far as an inductor (like a wire wound resistor) is concerned in modern circuits bigger is not better
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