Science & Engineering

Resistor Series Parallel Calculator

Finds the combined resistance of two resistors in series (R1 + R2) and in parallel (R1 x R2 / (R1 + R2)). Enter 100 and 220 ohms to get 320 ohms in series and 68.75 ohms in parallel.

What this calculator does

The Resistor Series Parallel Calculator estimates your result instantly from the values you enter, using standard science & engineering formulas. Finds the combined resistance of two resistors in series (R1 + R2) and in parallel (R1 x R2 / (R1 + R2)). Enter 100 and 220 ohms to get 320 ohms in series and 68.75 ohms in parallel. Calculations run in your browser, so nothing you type is sent to a server, and the output is an estimate rather than a certified or official figure.

Resistor Series/Parallel Calculator

Result

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Series Total (Ω)
—
Parallel Total (Ω)

About Resistor Series Parallel Calculator

Enter two resistor values and this tool returns both the series total (R1 + R2) and the parallel total (R1R2 / (R1 + R2)) in ohms. It is handy for quickly checking a two-resistor network.

Formula & Mathematical Calculation

Series Total (Ω) = f(Resistor 1 (Ω), Resistor 2 (Ω))

Calculated according to standard science formulas implemented in the calculator core.

Calculation Example

With R1 = 100 Ω and R2 = 220 Ω: series = 100 + 220 and parallel = (100 × 220) / 320. The Series Total box shows 320 Ω and the Parallel Total box shows 68.75 Ω, with the note In series: 320 Ω. In parallel: 68.75 Ω.

Key Benefits

  • Calculates both series and parallel totals for two resistors at once
  • Uses R1 + R2 for series and R1*R2/(R1+R2) for parallel
  • Rounds both totals to three decimal places in ohms
  • Rejects negative resistance values

How to Use this Calculator

  1. Enter Resistor 1
    Type the first resistance in ohms into the Resistor 1 field.
  2. Enter Resistor 2
    Type the second resistance in ohms into the Resistor 2 field.
  3. Calculate
    Click Calculate and read the Series Total and Parallel Total boxes.

Assumptions & Limitations

What the calculation assumes

  • Every value you enter is treated as an exact, known amount.
  • Any rate or interval you enter is assumed to hold for the whole period unless the form asks for it separately.
  • Results use standard published formulas and account only for the values entered above.
  • Rounding is applied for display; the underlying calculation uses your full precision.
  • Results are returned in the same units you enter, unless the tool states the output unit.

What it does not cover

  • Resistor Series Parallel Calculator produces a calculated result for reference and learning, not a certified or official measurement.
  • Real-world outcomes differ when tolerances, rounding rules or local standards apply.
  • Definitions and standards vary by region and change over time; verify the convention that applies to your case.
  • Figures are only as accurate as the inputs you supply — check them before acting on the result.
  • For work where the result carries real consequences, confirm it against an authoritative source.

Frequently Asked Questions

No, it takes exactly two resistor values, Resistor 1 and Resistor 2.

The parallel total is R1 x R2 / (R1 + R2), the product-over-sum rule for two resistors.

The parallel total is returned as 0 in that case, since the tool guards against dividing by a zero sum.

No. If either value is negative the tool shows an error that resistance cannot be negative.

Free to use, no account needed. Calculations run in your browser, so nothing you type is sent to a server. Results are estimates — how we build and check our calculators.