How to use this calculator
- Enter or choose connection.
- Enter or choose resistor values.
- The equivalent resistance updates as you type. Use Copy result or Share to keep it.
Method
Series: R = R₁ + R₂ + … + Rₙ; Parallel: 1/R = 1/R₁ + 1/R₂ + … + 1/Rₙ
- R₁ … Rₙ
- individual resistances in ohms
Worked example
- Series: 100 + 220 + 470 = 790 Ω.
- Parallel: 1/100 + 1/220 + 1/470 = 0.0100 + 0.004545 + 0.002128 = 0.016673 S.
- R = 1 ÷ 0.016673 = 59.98 Ω.
100 Ω, 220 Ω and 470 Ω give 59.98 Ω in parallel and 790 Ω in series.
What the result means
For mixed networks, reduce the circuit step by step: combine each parallel group, then add the groups in series.
Assumptions and limits
- Ideal resistors at their nominal values.
- Tolerance (±1% or ±5%) and temperature drift are not included; use the Resistor Calculator to read colour bands.
Questions
Why is parallel resistance smaller than any single resistor?
Each extra path lets more current flow for the same voltage, which is what lower resistance means.
Two equal resistors in parallel?
Half of one: two 100 Ω resistors in parallel make 50 Ω.