# What size resistor to choose?

Discussion in 'General Electronics Discussion' started by AndreeU17, Jul 27, 2014.

1. ### AndreeU17

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1
Apr 23, 2014
Its very basic question i know, however, i was curious as to what size resistor would we need for specific schematic. I'm not sure how to test whether i need a resitor around 100 Ohms or 1M Ohms. How do i test what resistor i need? I know i need to know the voltage that will be running thru the circuit but how can i check to see if i need a big resistor or small value resistor.

2. ### Harald KappModeratorModerator

10,836
2,443
Nov 17, 2011
R=V/I
If you know the voltage V and the current I, you calculate R. Or calculate V or I if you know the 2 other parameters.

For more in-detail help we need to see the schematic of the respective part of your circuit and a short explanation what this part of the circuit is expected to do.

3. ### Anon_LG

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117
Jun 24, 2014
It depends on the power rating of the component, this will be in watts if you want a more detailed explanation on how resistance affects the current see here. Post the schematic and what you want it to do.

4. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,449
2,809
Jan 21, 2010
When I think of "size" for a resistor, I think of power rating. The value in ohms is, well, the value of the resistor.

In general you don't "know" what value is required, you calculate it. Harald is 100% correct in saying that we need to see the circuit because there are many different calculations depending on exactly what the resistor has to do.

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