Skip to content
OneKitly
Sign up · Sign in

Series resistor calculator

Compute the total resistance of resistors connected in series.

Related tools

All Electronics tools →
Parallel resistor calculatorCompute the total resistance of resistors connected in parallel.Series capacitor calculatorCompute the total capacitance of capacitors connected in series.LED resistor calculatorFind the series resistor needed to drive an LED from a supply voltage.Resistor Color Code CalculatorDecode 4, 5 and 6-band resistor color codes into resistance, tolerance and temperature coefficient.Antenna length calculatorCut an antenna to the right size for any frequency. From the wavelength λ = c/f and a velocity factor, it sizes a half-wave dipole, quarter-wave vertical, 5/8-wave vertical or full-wave loop, returning the total length and the per-element length in both metres and feet.Impedance calculator (RLC)Compute the impedance of a series or parallel RLC circuit at any frequency. From R, L, C and f it returns the inductive and capacitive reactances, the impedance magnitude |Z|, the phase angle and the resonant frequency where the reactances cancel.PCB trace width calculator (IPC-2221)Size a printed-circuit-board trace for a given current using the IPC-2221 standard. Enter the current, the allowed temperature rise, the copper weight and whether the trace is external or internal, and it returns the required width in mils and millimetres — plus resistance and voltage drop if you give a length.Capacitor energy calculatorCompute the energy stored in a capacitor from its capacitance and voltage (E = ½CV²).

The Series resistor calculator turns Resistances (Ω, comma-separated) into Total resistance (Ω), instantly and for free. For instance, with Resistances (Ω, comma-separated) = 100, 220, 330 it returns Total resistance (Ω) = 650.

How to use it

  1. Enter your values: Resistances (Ω, comma-separated).
  2. Read the result instantly: Total resistance (Ω).

Frequently asked questions

How does the Series resistor calculator work?

It takes Resistances (Ω, comma-separated) and derives Total resistance (Ω) from them. The calculation is live as you type, so the result updates on every change.

Which values does the calculator ask for?

A single value: Resistances (Ω, comma-separated). Nothing else is required — no account, no file upload.

What does a typical calculation look like?

With Resistances (Ω, comma-separated) = 100, 220, 330, the calculator returns Total resistance (Ω) = 650. Those figures come from running this exact tool, so you can reproduce them by entering the same values.

How much does the result change with different inputs?

It moves a lot. Using Resistances (Ω, comma-separated) = 100, 231, 363 instead, Total resistance (Ω) goes from 650 to 694 — which is why it is worth testing a few scenarios rather than trusting a single figure.

What does it give for smaller values?

Scaled down to Resistances (Ω, comma-separated) = 100, 220, Total resistance (Ω) comes out at 320. The relationship is worth checking at both ends before you rely on a single result.

When would I actually use this?

At the bench: sizing a resistor for an LED, reading a colour band, working out a divider ratio, and checking a part will not cook.

What is the most common mistake?

Choosing a resistance and forgetting the power rating. A value that is electrically right will still burn if the package cannot dissipate what passes through it — check the watts as well as the ohms.

Is there a tool for the next step?

Series capacitor calculator is the closest one after this: Compute the total capacitance of capacitors connected in series.

What else is worth having open alongside it?

LED resistor calculator and Resistor Color Code Calculator — they come up in the same task often enough to be worth a second tab.

Where do the figures come from, and how current are they?

Ohm's law and the divider formulas are exact. Colour bands follow the IEC standard; real components carry a tolerance, so a nominal value and a measured one will not match exactly.

Further reading

All guides →
ExplainerResistors in Series and in Parallel: The Formulas, and the Three Things They Do Not Tell YouSeries adds, parallel adds reciprocals — that part is easy. The parts that catch people: which member dominates the answer, why two 5 % resistors in parallel are still 5 %, and why the smallest resistor in a parallel pair takes the largest share of the power.ExplainerCapacitors in Series: the Smallest One Decides, and Then It Fails100, 220 and 330 µF in series come to 56.9 µF — less than the smallest. Put 100 µF and 1 µF in series and the total is 0.99 µF, while the small one carries 99 % of the voltage.ExplainerA Capacitor Marked 220 Is Twenty-Two PicofaradsThe three digits are two figures and a count of zeros, in picofarads: 104 is 100 nF and 473 is 47 nF. The trap is 220, which is 22 pF — while a 220 pF part is marked 221.ExplainerThe Voltage Divider: The Formula Is Trivial, the Assumption Behind It Is NotVout = Vin·R2/(R1+R2) is only true when nothing is connected to the output. Draw current and the voltage collapses, by an amount that follows one exact law. Here is that law, the ten-times rule checked against it, and why a lower-resistance divider costs you power forever.How-toHow to Calculate an LED Series ResistorSize the series resistor for any LED with one formula: R = (Vs − Vf) / I. Follow the steps, see a worked 5 V example, and pick the right resistor.ExplainerWhat Is Ohm's Law? V = I × R Explained SimplyOhm's law links voltage, current, and resistance with one equation: V = I × R. Learn the triangle trick and see worked examples.