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.
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