The calculation, without hidden assumptions
Series and parallel resistor networks use different rules. Series values add directly; parallel branches add as reciprocals. This calculator keeps both in one canonical page and optionally applies Ohm’s law to the equivalent resistance when you enter a source voltage.
How to use this calculator
Choose series or parallel.
Enter two to four resistor values in ohms; leave unused optional values at zero.
Optionally enter source voltage to see the ideal total network current from the equivalent resistance.
Where people use it
- •Electronics bench calculations
- •Checking resistor combinations
- •Teaching series/parallel circuit relationships
Example: 100 Ω and 200 Ω in parallel
1/Req = 1/100 + 1/200 = 0.015, so Req is about 66.67 Ω.
What the result does not assume
- •The model assumes ideal resistors. Tolerance, temperature, source limits and component power ratings are separate design checks.
- •A zero-ohm branch is not accepted as an ordinary parallel input because it represents an ideal short circuit.
Frequently asked questions
Do resistors add in series?+
Yes. Ideal series resistance is the sum of all resistor values.
Why is parallel resistance lower than the smallest resistor?+
Adding parallel branches provides more current paths, so equivalent resistance falls below each positive branch resistance.
Can this calculate resistor power?+
This page focuses on equivalent resistance and optional total current; component power distribution requires the actual network voltages/currents.
Semantic next steps
Continue the calculation
These links move to a different input, formula or project stage rather than a keyword variation of this page.
Ohm's Law Calculator — Volts, Amps, Ohms and Watts
Calculate voltage, current, resistance and power from any two positive electrical values using Ohm's Law and Watt's Law.
OpenVA to Watts Calculator — Apparent vs Real Power
Convert volt-amperes to watts or watts to VA using an explicit power factor, while keeping apparent power and real power separate instead of treating them as interchangeable.
OpenThree-Phase Power Calculator — kW, kVA, kVAR & Power Factor
Calculate balanced three-phase apparent, real and reactive power from line-to-line voltage, current and power factor, with phase angle shown for the simplified power triangle.
OpenSeries & Parallel Capacitor Calculator — Equivalent Capacitance
Calculate equivalent capacitance for up to four capacitors in series or parallel, with the reciprocal relationship and optional stored-energy estimate from an entered voltage.
OpenRC Time Constant Calculator — Solve τ, R or C + Cutoff & Timing
Calculate RC time constant from resistance and capacitance or solve backward for resistance or capacitance from a target tau, with five-tau settling, first-order cutoff and charge/discharge timing.
OpenLED Resistor Calculator — E12/E24 Value, Color Code & Power
Calculate a simple DC LED current-limiting resistor, round upward to E12/E24, recalculate actual current and power, and show the selected resistor’s standard 4-band color code.
OpenReactance Calculator — Inductive XL, Capacitive XC & LC Resonance
Calculate inductive or capacitive reactance, reverse-solve frequency or component value, or find ideal LC resonant frequency with engineering-unit inputs and visible formulas.
OpenInternal Resistance Calculator — Battery Load Test, Two Points & Voltage Sag
Estimate a source or battery internal resistance from open-circuit and loaded voltage, from two load points, or run the internal-resistance model forward to check sag, loss and efficiency.
OpenMore in this calculator collection
Browse nearby calculators in the same topic cluster so related pages reinforce each other instead of sitting as isolated URLs.
Free publisher widget
Put this calculator on your website
Give readers the live calculator without rebuilding the math. Copy the responsive embed in one click, or customize width, height, border and corner radius before publishing. The branded MAXScanner attribution stays visible.
Calculator embed HTML
Paste this code into your page. Focus the code box to select it manually.
Keep the result connected to the real job
MAXScanner keeps the formula and assumptions beside the result so you can verify the number before using it in a drawing, estimate, specification, worksheet or document. Where a supplier, manufacturer, drawing or applicable standard owns a requirement, that source remains authoritative.