Resistor Network Calculator - Series and Parallel Resistance

Agarapu Ramesh — Editor and content reviewer
Editorially reviewed Reviewed by Agarapu Ramesh, science educator (chemistry). LinkedIn
Last reviewed: May 2026 | Standard electrical engineering formulas

Series resistors add straight across. Parallel resistors do not. In parallel, the total resistance is lower than the smallest branch, which is exactly where beginners get caught.

Formula at a glance

  • series: Rtotal = R1 + R2 + ...
  • parallel: 1 / Rtotal = 1 / R1 + 1 / R2 + ...
  • two parallel: Rtotal = R1 x R2 / (R1 + R2)

Field note: A calculator gives the ideal value. On the bench, tolerance, heat and layout can move the result.

Ω

Resistor Network Calculator

Series & parallel resistance calculator

Enter values separated by commas or spaces (up to 10 resistors)

Result
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Formulas

SeriesR = R₁ + R₂ + R₃ + ...
Parallel1/R = 1/R₁ + 1/R₂ + ...
2 ParallelR = (R₁×R₂)/(R₁+R₂)

Quick Tips

Series:
• Current same through all
• Voltage divides
• R_total > any R

Parallel:
• Voltage same across all
• Current divides
• R_total < smallest R

Related

Ohm's LawCurrent DividerVoltage Divider

How to use the Resistor Network Calculator

Use this as a bench check, then compare it with the part marking, tolerance and a meter reading when the circuit matters. Small components are cheap. Bad assumptions are not.

Worked example

Example: 100 ohm and 200 ohm in series gives 300 ohm. The same two in parallel give 66.7 ohm.

Practical checks before you trust the number

  • Check resistor power in each branch, not just total resistance.
  • Tolerance stacks up in networks.
  • For low-ohm power resistors, lead resistance can matter.

Common mistake

A calculator gives the ideal value. On the bench, tolerance, heat and layout can move the result.

Sources and references

Related calculators

Frequently Asked Questions

Series resistance: R_total = RI + RI + RI + ... Just add. Example: 100 Ω + 220 Ω + 470 Ω = 790 Ω in series. Current is the same through all; voltage divides proportionally. Used in voltage dividers, current limiters, and bias networks.

Parallel resistance: 1/R_total = 1/RI + 1/RI + 1/RI + ... Or for two resistors: R_total = (RI × RI) ÷ (RI + RI). Example: 100 Ω in parallel with 200 Ω = (100 × 200) ÷ 300 = 66.7 Ω. Voltage is the same across all; current divides inversely with resistance.

Series: just add up. Parallel: reciprocal sum, or product-over-sum for two. Combinations: simplify each parallel branch first, then add the series. Or vice versa. Always work from the innermost group outward.

Identify clusters of resistors that are purely series or purely parallel; reduce each cluster to a single equivalent. Repeat until you have one final value. Example: RI in series with (RI I RI) → first compute RI I RI, then add RI. Practice on schematic worksheets — speed comes with repetition.

Because in parallel, multiple paths share the current. The combined resistance is always less than the smallest one. Two 10 Ω resistors in parallel = 5 Ω. Five 10 Ω resistors in parallel = 2 Ω. The more paths, the less total opposition to current flow.

Use Ohm's law and Kirchhoff's laws. For series: I = V_total ÷ R_total, same I through all. For parallel: V is the same across each, so I per branch = V ÷ R_branch. For mixed networks, simplify to total R first, find total I, then back-substitute branch by branch.

Yes. Enter series and parallel groupings; the calculator returns total resistance, and often per-branch currents and voltages. Useful for verifying hand calculations and for designing voltage dividers, attenuators, and load matching networks. Always sanity-check against rough estimates.