電阻串聯・並聯計算

How to use this calculator

1. Type the resistor values in ohms, separated by commas, spaces or new lines.
2. Choose series or parallel.
3. Click Calculate for the total resistance.

Handy shortcuts

• Two equal resistors in parallel give half the value (two 100 Ω → 50 Ω).
• Two equal resistors in series give double the value.
• The parallel total is always smaller than the smallest resistor.

Series and parallel formulas

Resistors in series add up:

Resistors in parallel combine as the reciprocal of the sum of reciprocals:

The parallel total is always smaller than the smallest resistor in the group, while the series total is the simple sum.

常見問題

How do I calculate resistors in parallel?

Add the reciprocals and invert: 1/Rtotal = 1/R₁ + 1/R₂ + … For two resistors, Rtotal = R₁R₂/(R₁+R₂).

What is the total of two 100 Ω resistors in parallel?

50 Ω — two equal resistors in parallel give half the value.

Series or parallel — which is bigger?

Series adds up to a larger total; parallel always gives less than the smallest resistor in the group.