# Electronics notation - what does R1//R2 mean?

**URL:** <https://boards.straightdope.com/t/electronics-notation-what-does-r1-r2-mean/749151>\
**Category:** Factual Questions\
**Created:** [March 16, 2016, 11:41am UTC](https://boards.straightdope.com/t/electronics-notation-what-does-r1-r2-mean/749151 "2016-03-16T11:41:49Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\
**Post date:** [March 16, 2016, 11:41am UTC](https://boards.straightdope.com/t/electronics-notation-what-does-r1-r2-mean/749151/1 "2016-03-16T11:41:49Z")

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Well, the question is in the title really. Never come across “//” before. Can’t seem to find a google search that will pull it up, probably because of the ubiquity of “//”.

For context, see [here](http://www.ti.com/ww/en/bobpease/assets/AN-31.pdf)

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**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\
**Post date:** [March 16, 2016, 11:46am UTC](https://boards.straightdope.com/t/electronics-notation-what-does-r1-r2-mean/749151/2 "2016-03-16T11:46:42Z")

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In parallel.

The circuit is fed from a set of voltage sources - so the impedance of the sources is zero. Thus the resistors all appear in parallel for the purposes of calculating the gain etc.

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**Author:** ![Tatterdemalion](https://avatars.discourse-cdn.com/v4/letter/t/43a26b/32.png) [@Tatterdemalion](https://boards.straightdope.com/u/Tatterdemalion)\
**Post date:** [March 16, 2016, 11:47am UTC](https://boards.straightdope.com/t/electronics-notation-what-does-r1-r2-mean/749151/3 "2016-03-16T11:47:41Z")

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> [@Princhester](#):
>
> Well, the question is in the title really. Never come across “//” before. Can’t seem to find a google search that will pull it up, probably because of the ubiquity of “//”.
> 
> For context, see [here](http://www.ti.com/ww/en/bobpease/assets/AN-31.pdf)

It means r1 in parallel with r2.

It’s shorthand for 1/(1/r1 + 1/r2).

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<div class="post-metadata">

**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\
**Post date:** [March 16, 2016, 11:55am UTC](https://boards.straightdope.com/t/electronics-notation-what-does-r1-r2-mean/749151/4 "2016-03-16T11:55:16Z")

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Huh, thanks guys. That’s what I thought it should be, but then everywhere I tried to look it up suggested that parallel was “||” not “//” so I thought it had to be something different.

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**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\
**Post date:** [March 16, 2016, 2:25pm UTC](https://boards.straightdope.com/t/electronics-notation-what-does-r1-r2-mean/749151/5 "2016-03-16T14:25:53Z")

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Both are used, but I think // is common in engineering because || looks too much like 11.