# Resistance in Parallel Circuts.

**URL:** <https://boards.straightdope.com/t/resistance-in-parallel-circuts/56943>\
**Category:** Factual Questions\
**Created:** [March 6, 2001, 3:55pm UTC](https://boards.straightdope.com/t/resistance-in-parallel-circuts/56943 "2001-03-06T15:55:02Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![Dr.Ferret](https://avatars.discourse-cdn.com/v4/letter/d/f1d935/32.png) [@Dr.Ferret](https://boards.straightdope.com/u/Dr.Ferret)\
**Post date:** [March 6, 2001, 3:55pm UTC](https://boards.straightdope.com/t/resistance-in-parallel-circuts/56943/1 "2001-03-06T15:55:02Z")

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Hi Team! For people with elctrical experience.

What is the simplest method for calculating resistance on parallel circuits?? best formula?

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**Author:** ![KeithB](https://avatars.discourse-cdn.com/v4/letter/k/48db29/32.png) [@KeithB](https://boards.straightdope.com/u/KeithB)\
**Post date:** [March 6, 2001, 4:02pm UTC](https://boards.straightdope.com/t/resistance-in-parallel-circuts/56943/2 "2001-03-06T16:02:13Z")

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If you want to keep working with them as resistances, and not conductances, there is only one formula:

1/(1/R1 + 1/R2 + 1/R3…)

If you are working with known resistors you can simplify things a bit. If you have 2 resistors of the same value the parallel combination is 1/2 the resistance of one of them, for example.

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**Author:** ![Dr.Ferret](https://avatars.discourse-cdn.com/v4/letter/d/f1d935/32.png) [@Dr.Ferret](https://boards.straightdope.com/u/Dr.Ferret)\
**Post date:** [March 6, 2001, 4:08pm UTC](https://boards.straightdope.com/t/resistance-in-parallel-circuts/56943/3 "2001-03-06T16:08:25Z")

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Thankyou Keith, MUCH appreciated!!

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**Author:** ![erislover](https://avatars.discourse-cdn.com/v4/letter/e/71e660/32.png) [@erislover](https://boards.straightdope.com/u/erislover)\
**Post date:** [March 6, 2001, 4:29pm UTC](https://boards.straightdope.com/t/resistance-in-parallel-circuts/56943/4 "2001-03-06T16:29:12Z")

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For two resistances (r[sub]1[/sub]+r[sub]2[/sub])/(r[sub]1[/sub]\*r[sub]2[/sub])  
Sum over product.

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**Author:** ![Patty\_O\_Furniture](https://avatars.discourse-cdn.com/v4/letter/p/96bed5/32.png) [@Patty\_O\_Furniture](https://boards.straightdope.com/u/Patty_O_Furniture)\
**Post date:** [March 6, 2001, 4:47pm UTC](https://boards.straightdope.com/t/resistance-in-parallel-circuts/56943/5 "2001-03-06T16:47:49Z")

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The opposite of what **aynrandlover** lover said.

Product over the sum.

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**Author:** ![Dr.Ferret](https://avatars.discourse-cdn.com/v4/letter/d/f1d935/32.png) [@Dr.Ferret](https://boards.straightdope.com/u/Dr.Ferret)\
**Post date:** [March 6, 2001, 5:05pm UTC](https://boards.straightdope.com/t/resistance-in-parallel-circuts/56943/6 "2001-03-06T17:05:18Z")

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Thanks again team!