How To Calculate Resistors In Series And Parallel - Kitronik

Maybe your like

Kitronik

Weather Notice: DPD are advising of delays in some areas due to current weather conditions, check here to see if your ara is effected.

Share 29 comments

Resistors in Series

When resistors are connected one after each other this is called connecting in series. This is shown below. resistors_in_series_1

To calculate the total overall resistance of a number of resistors connected in this way you add up the individual resistances. This is done using the following formula: Rtotal = R1 + R2 +R3 and so on. Example: To calculate the total resistance for these three resistors in series.

Rtotal = R1 + R2 + R3 = 100 + 82 + 1 Ohms = 183 Ohms

Task 1:

Calculate the total resistance of the following resistor in series.

	Rtotal	= _______________
		= _______________

	Rtotal	= _______________
		= _______________

	Rtotal	= _______________
		= _______________

Resistors in Parallel

When resistors are connected across each other (side by side) this is called connecting in parallel. This is shown below. resistors_in_series_6

Two Resistors in Parallel

To calculate the total overall resistance of a of two resistors connected in this way you can use the following formula:

Example: To calculate the total resistance for these two resistors in parallel. resistors_in_series_8

Task 2:

Calculate the total resistance of the following resistor in parallel. resistors_in_series_9

Three or more resistors in parallel

To calculate the total overall resistance of a number of three or more resistors connected in this way you can use the following formula: resistors_in_series_11

Example: To calculate the total resistance for these three resistors in parallel resistors_in_series_12

Task 3:

Calculate the total resistance of the following resistor in parallel. resistors_in_series_13

Answers

Task 1

1 = 1492 Ohms 2 = 2242 Ohms 3 = 4847 Ohms

Task 2

1 = 5 Ohms 2 = 9.57 Ohms 3 = 248.12 Ohms

Task 3

1 = 5.95 Ohms 2 = 23.76 Ohms Download a pdf version of this page here

Learn more about the author read more »

©Kitronik Ltd – You may print this page & link to it, but must not copy the page or part thereof without Kitronik's prior written consent.

Kitronik's suggested additional learning

How A Potential Divider / Voltage Divider Works

Two or more resistors when connected in series make up a potential divider circuit, this tutorial explains how they work and the voltage across them. Circuit diagrams, formulas, worked examples and some questions to test your understanding are included in the tutorial.

Tags: Electronic principles, Understanding components, Understanding principles Share

29 comments

Jhayvir

18 June 2020 at 12:36pm

What is the equivalent resistance of the three resistors in series with the following values: R1 = 10 Ω, R2 = 20 Ω, and R3 = 5 Ω (Give only the numeric part of your answer.)

Can u guys hep me? Please thanks for the response :>

Mark Donnison

27 June 2019 at 16:07pm

Hi, without seeing how your classmate is arriving at an answer it is impossible to say. However, this is the correct way and if you do it this way you know that you will arrive at the correct answer. I hope this helped.

Thea

17 June 2019 at 12:41pm

Hi! I'm confused because the method my classmate use in solving Parallel Resistors are different from this. I prefer this method because I can understand it well and used this when I'm in Grade 5. So my question is do we get the same answer if I use this method and my classmates will use the method where they will find its denominator?

kaola

08 June 2019 at 04:36am

thank you

Mark Donnison

07 June 2019 at 08:24am

Hi!

Justin chow

29 May 2019 at 06:41am

hi mark

Mark Donnison

24 May 2019 at 10:50am

Hi, there is a worked example that shows how to insert your values into the formula and how to take it forwards to an answer. Which bit of the process isn't clear, perhaps we can look at editing the example to highlight this.

no explanation

24 May 2019 at 03:21am

no explanation on the calculation for the 3 parallel resistor, pointlesss, just hocus pocus and assume everyone gets it

dajake

25 February 2019 at 09:04am

nice calculations

Sanjay

05 December 2018 at 06:47am

Really I will your instructions is a very helpful .thanks a lot sir

Tom

14 September 2018 at 11:19am

Just for fun: task 3 example 1 should be 6 Ohms Also formula for two res in paralel and for more than 2 is exactly the same – if you use the latter for two, but solve it with vulgar fractions without finding smallest denominator, you will get the same formula. So, its also possible to make formulas for each on n numbers of resistors, but its impractical for normal use. P.e. for 3 res Rtot=R1xR2xR3/((R1xR2)(R2xR3)(R1xR3))

Mark Donnison

17 July 2018 at 13:22pm

Hi, thanks for getting in touch. The information that you require is included in the above tutorial. Where it says 'and so on', this indicates that the process is the same for additional resistors. I hope this helps.

sikander lal walia

13 July 2018 at 07:21am

How to calculate the value of 3 and more resistors in parallel and elaborate the same.

Mark Donnison

04 June 2018 at 13:13pm

Hi Ian, it's difficult to visualise your circuit without seeing it but I will give an answer based on what I think you have. Firstly, you will need to work out the value of the three resistors in parallel (the formula is on the page above). Then, once you have this value you then need to do an in series calculation using the resistor on its own and the result of the first calculation you did to give the total resistance for the circuit. I hope this helps.

Ian De La Cruz

01 June 2018 at 22:21pm

I need your help to find the correct formula . I have 3 parallels and one other on its own. I’m sorry I don’t know the correct terminology but all have a value of 60 ohms . I got an A side and B side : on the A side I have the 60 alone and on the B side I have 3 – 60 ohms. I’m pretty good at math but the formula is missing here. Please help me with a formula to figure out the total resistance

Patrick Lummumba Sunu

27 May 2018 at 21:37pm

This is awesome

danburite

28 March 2018 at 17:39pm

thanks,mark.

Mark Donnison

05 July 2017 at 11:19am

Hi Yonela, yes you need to use a different formula as is shown in the worked examples.

yonela

29 June 2017 at 08:30am

for parallel circuit with two resistor we only use that formula in task 2 we do not use it when we have three or more resistors?

Mark Donnison

03 April 2017 at 11:05am

Hi Bill, you would use the series calculation first to find the combined resistances. So, in this case, R1 becomes R1Total and R2 becomes R2Total and you can then do the parallel calculation as normal. I hope this helps.

Bill

28 March 2017 at 16:13pm

so for parallel circuits with >2 resistors, there is no algebraic equation derived that we can use. We only do the specific calculation to find the specific answer every time?

Mark Donnison

13 October 2016 at 15:43pm

Hi Tom, If your target is 15 the calculation would look like; 1/15 = 1/48 + 1/80 + 1/R. Then rearrange the formula for R, it becomes; 1/15 – 1/48 – 1/80 = 1/R.

Tom

12 October 2016 at 16:52pm

Hi i read this reply to colin and didnt quite understand. What do you do once you have the reciprical values for example my taget is 15 i have 2 resisitors 48 and 80. Recipricals are 1/48=0.208333333 and 1/80=0.0125 what do i do from here?

Manuna Kawkni

16 July 2016 at 00:21am

very important in my training.

Edwin mothibeli

26 May 2016 at 07:20am

This is very helpful,thank you for the initiative

Rob Haywood

28 January 2016 at 09:32am

Hi Colin, Simply work the formula backwards. For series start with the value you want to achieve, subtracting values you have as you go until you reach 0. For parallel what we're dealing with is reciprocal numbers, and they can be reversed. For example 1/33 = 0.30303. 1/0.30303 = 33. So start with the value you want to achieve. Take a resistor value you have and divide 1 by that value to get the reciprocal number. Rob

Colin gilly

27 January 2016 at 23:12pm

What is the formula if I know what resistance I want to achieve but don't have the correct value available. But I do have lots of other value resistors that I might be able to use?

Rob Haywood

27 February 2015 at 13:31pm

HI Elias, It comes down to rounding. We rounded to three significant figures, but if you round shorter than that you will see an answer of around 6, so you have done it right. Given the value of standard resistors anyway in this case you would probably use 6.8 Ohms. Hope that helps.

elias mellber

09 February 2015 at 09:48am

Hi! I was just wondering about these parallel resistor equations. Isn't the answer to Task 3 question 1 suppose to be 6 instead of 5.95? Or am I just totally lost here? Have a good one!

Kitronik Newsletter

Interests

Coding, Computer Science & micro:bit
DT & Project Kits
Materials

Your email Subscribe

100% free, Unsubscribe any time!

Latest Resources

The Kitronik Book of Design & Technology Projects Volume 5Book of Makes3 Jan 2026
Happy New Year from Kitronik for 2026 — We’re Back!News2 Jan 2026
Laser Cut Black Painted MDF Fridge MagnetsMaker tutorials31 Dec 2025
Laser-Cut Cathedral Radio style Mono Amp Kit enclosureMaker tutorials30 Dec 2025
Bauhaus-Inspired Finnboard ClockMaker tutorials29 Dec 2025

Free UK Delivery*

Spend over £50 (ex VAT) and get free delivery. (excludes sheet materials and offshore / remote areas).

No Quibble Refunds

If you don't like the product for whatever reason, send it back (packaged and unused) for a full refund.

Product Support

Free Email and telephone support on all our products.

Secure Payments

Pay securely using credit / debit card or by Paypal.

Tag » How To Find The Resistance

How To Calculate Resistors In Series And Parallel - Kitronik

Resistors in Series

Task 1:

Resistors in Parallel

Two Resistors in Parallel

Task 2:

Three or more resistors in parallel

Task 3:

Answers

Task 1

Task 2

Task 3

Kitronik's suggested additional learning

How A Potential Divider / Voltage Divider Works

Kitronik Newsletter

Calculating Resistance – Ohm's Law - Current, Voltage And ... - BBC

4 Ways To Calculate Total Resistance In Circuits - WikiHow

Ohms Law Tutorial And Power In Electrical Circuits

How To Calculate Resistance Using Resistivity | Physics

Calculating Total Resistance In Circuits - YouTube

Calculating Resistance - YouTube

Resistivity And Conductivity - Hyperphysics

Electrical/Electronic - Series Circuits

Resistance And Resistivity | Physics - Lumen Learning

Resistor Calculator

What Is Ohm's Law And How Do You Calculate Resistance Equations?

Specific Resistance | Physics Of Conductors And Insulators

Ohm's Law For Beginners And Novices

9.4: Resistivity And Resistance - Physics LibreTexts

Contact