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Resistors in series calculator
Electricity
The total resistance of two resistors connected in series is the sum of their resistances.
Rtotal = R1 + R2
This free calculator is for GCSE and A-level physics. Choose the quantity you want to find, enter the other values with their units, and it shows the working in the layout used in exams, with the answer to the number of significant figures you choose. The values shown are an example. Change them to your own.
Quantity to find
Working
- Write the equationRtotal = R1 + R2
- Substitute the valuesRtotal = 47 + 100
- CalculateRtotal = 147 Ω
- Give the answer to 3 significant figuresRtotal = 147 Ω
Worked example
Find Rtotal, the total resistance. Given: resistance R1 = 47.0 Ω; resistance R2 = 100 Ω.
- Write the equationRtotal = R1 + R2
- Substitute the valuesRtotal = 47 + 100
- CalculateRtotal = 147 Ω
- Give the answer to 3 significant figuresRtotal = 147 Ω
Symbols and units
| Symbol | Quantity | SI unit |
|---|---|---|
| Rtotal | Total resistance | Ω |
| R1 | Resistance | Ω |
| R2 | Resistance | Ω |
Resistors in series: rearranged
- To find total resistance: Rtotal = R1 + R2
- To find resistance: R1 = Rtotal − R2
- To find resistance: R2 = Rtotal − R1
Exam tip
Add more resistors in the same way. The total is always bigger than the largest single resistor.
Common questions
What is the formula for resistors in series?
The equation is Rtotal = R1 + R2, where Rtotal is the total resistance (Ω); R1 is the resistance (Ω); R2 is the resistance (Ω).
What units should I use for resistors in series?
In SI units: total resistance in Ω, resistance in Ω, resistance in Ω. The calculator also accepts common alternatives such as kilometres, grams or minutes, and converts them for you.
How do I rearrange Rtotal = R1 + R2?
Rearranging gives these forms: to find total resistance: Rtotal = R1 + R2. to find resistance: R1 = Rtotal − R2. to find resistance: R2 = Rtotal − R1.
Practise resistors in series questions
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Related
More electricity equations: Charge, current and time, Ohm’s law, Electrical power, Electrical power, Energy transferred, Resistors in parallel, Resistivity, EMF and internal resistance. See the full list on the physics equation calculator page.