# Which resistor watt rating to use for this circuit and Arduino 5V?

http://www.skillbank.co.uk/arduino/measure.htm

I am looking to build the circuit this guy recommends for making a better analog reference source. I found the voltage reference diode, and now I am looking for the proper resistor. I found a few 560Ω resistors with 1% rating. Now I am wondering what wattage they should be set at.

I think, the amperage for the 5V output of the Arduino is 500mA or so. Can anyone comment on that? Is there a best resistor watt rating you would choose for this circuit?

Are using watt ratings too far above necessary - bad? Or is that ok? Or stupid? Why?

• I want an accurate voltage reference so I can better measure ADC sources - such as temperature on a TMP36 - as shown to everyone doing Arduino projects... but never properly explained to newbies as to why its so inaccurate. Posted again after trying to work in this related question: electronics.stackexchange.com/questions/94406/… – Tbarbe Sep 15 '14 at 12:40

Power dissipated at the resistor is really minuscule. $P=\frac{(V_{CC}-V_Z)^2}{R}\cong 1.5\, \mathrm{mW}$. It will not cause significant heating even in small 0402 resistor. Using a bigger resistor will make no difference.