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Series / Parallel Resistor Calculator

Build a resistor network, verify its real electrical stress, and tune it to a target with one practical extra resistor.

Network configuration
Resistors3/8
R1
R2
R3
Live circuit view
V112 VI = 1.519 mAR11 kΩR22.2 kΩR34.7 kΩReq = 7.9 kΩ

Equations

Req=R1+R2+⋯+RnR_{eq}=R_1+R_2+\cdots+R_n
I=VReqI=\dfrac{V}{R_{eq}}
Pi=I2RiP_i=I^2R_i
Electrical analysis
Equivalent resistance7.9 kΩ
Total current1.519 mA
Total power18.228 mW
Minimum Equivalent resistance7.505 kΩ
Maximum Equivalent resistance8.295 kΩ

Worst-case equivalent resistance for 5% equal-tolerance resistors.

Per-resistor stress budgetRecommended ratings include 2× margin
ResistorVoltageCurrentDissipationRecommended rating
R1 · 1 kΩ1.519 V1.519 mA2.307 mW63 mW
R2 · 2.2 kΩ3.342 V1.519 mA5.076 mW63 mW
R3 · 4.7 kΩ7.139 V1.519 mA10.844 mW63 mW
One-resistor tuning assistant

Enter the desired equivalent resistance. The assistant finds the exact and nearest E-series value for one added resistor.

Current error-21%
Add in series2.1 kΩ
Practical value (E24)2.2 kΩ
Expected equivalent10.1 kΩ

Power recommendations apply a 2× margin at the entered DC voltage. Confirm voltage rating, pulse capability, temperature derating and fault conditions before release.

Network guide

Analyse a resistor network, not just one value

Series and parallel combinations can obtain a value, spread dissipation, or tune impedance. Their reliability depends on tolerances, individual power ratings, and load behaviour.

Method and assumptions

In series, resistances add. In parallel, the inverse of the equivalent resistance is the sum of inverses. The tool also reports voltage, current, and power distribution to spot an overloaded component.

Inputs to verify

Topology

Select series to increase value or voltage withstand; parallel to lower value or share current.

Tolerance and power

Nominal values are not enough: check the tolerance case that increases power in a branch.

Recommended workflow

  1. 1Define the target resistance and applied voltage or current.
  2. 2Compare several E-series preferred-value combinations.
  3. 3Check dissipation, maximum voltage per part, tolerance, and availability before approval.

Checkable example

Two 1 kΩ resistors in series give 2 kΩ. The same resistors in parallel give 500 Ω; at the same voltage, each takes half the total current when their values match.

Limits to keep in mind

The calculation assumes linear resistors. At high frequency, parasitic inductance, working voltage, and PCB arrangement can make a combination unsuitable.

Frequently asked questions

Is power always shared equally in parallel?

Only for equal values at comparable temperature. Tolerance and temperature coefficient can unbalance sharing.

Why use two resistors instead of one?

It can provide an unavailable value, spread power, improve voltage withstand, or offer finer adjustment. It also adds failure points and board area.

References to consult

  • Method references: IEC 60063 preferred-number series, working-voltage ratings, and derating curves of the selected resistors.

Original educational content, reviewed for technical clarity on 20 August 2026. Always verify datasheets, applicable standards, and your design before power-up or manufacture.