Series & Parallel Resistor Calculator
Calculate the total equivalent resistance for any number of resistors wired in series or parallel. Results update live as you type.
How to Use This Calculator
Choose Series or Parallel mode, then enter your resistor values in ohms (Ω). Add more resistors with the button below the list. Values update live — no button press needed. Remove any resistor with the × button.
Formula
Series: Resistances simply add together.
Parallel: The reciprocal of the total equals the sum of reciprocals.
Where each Rn is a resistor value in ohms.
Example
R_total = 100 + 220 + 470 = 790 Ω
Parallel: 1 kΩ and 1 kΩ
1/R = 1/1000 + 1/1000 = 0.002 → R = 500 Ω
Frequently Asked Questions
When would I use resistors in series?
Series resistors increase total resistance and share the same current. They are used in LED strings, voltage dividers, and current-limiting applications where you need a specific total resistance from available parts.
When would I use resistors in parallel?
Parallel resistors decrease total resistance and share the current load. They are used when you need a resistance value lower than your smallest available resistor, or when you want to share power dissipation across multiple components.
Why is a parallel combination always less than the smallest resistor?
Adding any parallel path always gives the current more routes to flow through, which always reduces the total opposition to current — regardless of the values involved. The result is always less than the smallest individual value.
Can I mix series and parallel?
Yes — in complex circuits you can have series-parallel combinations. Solve the parallel sub-groups first to get an equivalent resistance, then treat those equivalents as series resistors in the main loop.