Resistance network tool
Series and Parallel Resistance Calculator
Calculate total resistance for simple two-resistor series or parallel circuit notes.
Calculate Series or Parallel Resistance
Choose series or parallel and enter two resistor values to calculate the equivalent resistance.
Result
Total resistance
320 ohm
Result notes
Keep the entered values, assumptions, and result together when adding this calculation to job notes or submittal records. Final installation choices should align with the applicable code edition, equipment listing, manufacturer instructions, local amendments, and AHJ requirements.
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Formula and field context
Calculate total resistance for simple two-resistor series or parallel circuit notes.
Formula context
Series Parallel Resistance Chart
Series resistances add directly: 100 ohm + 220 ohm = 320 ohm. Parallel resistance uses reciprocal sums: 330 ohm || 680 ohm is about 222 ohm. For a mixed circuit, 220 ohm in series with that 222 ohm section gives about 442 ohm before calculator current or wattage checks.
Formula
Series: Rtotal = R1 + R2 + R3. Parallel: 1 / Rtotal = 1 / R1 + 1 / R2 + 1 / R3.Variables to keep with the result
- Rtotal is equivalent resistance in ohms.
- R1, R2, and R3 are individual resistor values or already-reduced branch values.
- Parallel branch conductance is added through reciprocal resistance.
- Mixed networks are reduced one clear series or parallel section at a time.
Formula and variables
For two resistors in series, total resistance is Rtotal = R1 + R2. For two resistors in parallel, total resistance is Rtotal = (R1 x R2) / (R1 + R2). The series result is higher than either resistor, while the parallel result is lower than the smallest branch resistance. Use the same units for both resistor entries.
U.S. field context and example
This worksheet supports control-circuit notes, electronics troubleshooting, test resistor setups, shunt or burden review, and quick checks before moving into a larger series-parallel circuit. For example, 100 ohms and 220 ohms in series total 320 ohms. The same two resistors in parallel total about 68.75 ohms, so current and power distribution change significantly.
Assumptions and limits
The tool handles two ideal resistive values at a time. Real assemblies may include tolerance, temperature coefficient, wattage limits, lead resistance, contact resistance, and load interaction. Use the full series circuit, parallel circuit, or circuit-analysis calculator when more than two elements, mixed topology, voltage drops, branch currents, or power ratings need to be reviewed together.
Common mistakes
Common mistakes include treating parallel resistance like a simple sum, forgetting that the smallest branch dominates the parallel result, and using the equivalent resistance without checking power in each resistor. When the worksheet supports a field test or control-panel change, keep resistor wattage, tolerance, and measured values with the result.