Series/Parallel Resistor Calculator: Get Total Resistance Fast
Quick Start
- Select Series or Parallel.
- Enter resistor values (e.g., 100, 4.7k, 2M). Upper/lowercase is accepted.
- Add or remove rows as needed.
- Read the total resistance in Ω, kΩ, or MΩ.
Input Formats
- Accepts integers and decimals with k/K/M multipliers; Ω and spaces are optional.
- Invalid characters are ignored; blank rows are skipped.
How It Works
- Series: Rtotal = R1 + R2 + … + Rn
- Parallel: 1/Rtotal = 1/R1 + 1/R2 + … + 1/Rn
- Zero or negative values are treated as invalid and ignored.
Rounding and Units
Results are shown with sensible rounding; internal math uses full precision.
Worked Examples
- Series: 220 + 330 + 1k → 1.55 kΩ
- Parallel: 1k || 1k → 500 Ω
- Parallel: 4.7k || 10k → ~3.2 kΩ
Common Mistakes
- Mixing k and M (e.g., 4.7m vs 4.7M).
- Using commas or unusual separators.
- Entering zero or negative values.
- Expecting equal-value parallel to return the same value—it halves.
Tips for Design
- Combine series/parallel networks to hit targets between standards.
- Consider tolerance and power rating separately; this tool computes resistance only.
- More equal branches in parallel reduce the effective resistance.
FAQ
Can I leave some inputs blank?
Yes. Blanks are ignored.
How many resistors can I add?
A sensible upper limit prevents unwieldy inputs.
Why is the result slightly rounded?
For readability; calculations use full precision.
Do units matter?
Yes. Use k for kilo and M for mega.