# Resistor calculations

Discussion in 'General Electronics Chat' started by Webby, Oct 19, 2008.

1. ### Webby Thread Starter Active Member

Jun 15, 2008
66
0
Hi, with two resistors in parrallel circuit of the same value the equation

R1 X R2 divided by R1 + R2 = Total resistance

does this equation still apply if the resistors are of different value?

Jan 28, 2005
9,030
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3. ### mik3 Senior Member

Feb 4, 2008
4,846
63
Yes, but it applies only for two resistors in parallel. If you have more than two use this formula:

Requivalent=1/(1/R1+1/R2........+1/Rn)

4. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
That same trick can be used to tweak standard resistors to astandard values. Given 3 resistors you can get pretty close to any value you choose, as long as your meter is accurate and the resistors don't drift.

5. ### SgtWookie Expert

Jul 17, 2007
22,183
1,728
Here is an online calculator that's quite handy for determining combinations of two resistors in series or parallel to arrive at an equivalent resistance:
http://www.qsl.net/in3otd/parallr.html