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How it Works »New Instructable »I am relatively new to electronic projects building and I have noted that some projects do not state the power and tolerance of the resistors. How should I proceed, are there any guide lines to establish the tolerance and wattage? Thatnks.

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Power rating tells you the maximum current that you can put through the resistor before it burns up or explodes. For a resistor, P = I

^{2}R, so I(max) = sqrt(P/R). If that 1 kohm resistor above is rated at 1/4 watt, then the maximum current allowed is sqrt(0.25/1000) = sqrt(2.5×10^{-4}) = 1.58×10^{-2}= 15.8 mA.If the project you're buiding tells you how much current is involved, then you can work out what rating resistor you need.