Series / Parallel Resistor Calculator
Combine any number of resistors in series or parallel and get the equivalent resistance live.
What it does: Work out the total resistance of several resistors in series or parallel.
When to use it: When you don't have the exact value on hand and want to build a target from resistors you already have.
Compute the equivalent resistance? of several resistors.
MEANS The equivalent resistance of these — resistors is —.
Common cases pre-computed: browse series & parallel resistor presets →
No history yet. Each calculation is automatically saved to this device.
How to use the series/parallel resistor calculator
Pick the mode → enter values → read the total.
- 01
Pick the connection type
Series = connected end to end (resistances add up); parallel = joined at both ends (conductances add up).
- 02
Enter each resistor value
Accepts
1k,4.7k,220notation. Click "+ Add resistor" if you need more. - 03
Read the total resistance
The result updates live. Expand to see the step-by-step sum / reciprocal sum.
Series / parallel cheat sheet
The two connections work in opposite directions — don't mix them up.
| Connection | Formula | Result trend |
|---|---|---|
| Series | R = R₁ + R₂ + … | Total goes up (≥ the largest one) |
| Parallel | 1/R = 1/R₁ + 1/R₂ + … | Total goes down (< the smallest one) |
| Two in parallel | R = R₁·R₂ / (R₁+R₂) | Handy quick formula |
Derived from Ohm's law and Kirchhoff's laws.
Common questions, answered in 3 minutes
Why does parallel resistance get smaller?
You've opened another path for current, so the whole thing conducts more easily — the equivalent resistance is always smaller than the smallest individual resistor.
What do two 1k resistors in series equal?
2k. Series is just simple addition.
And two 1k in parallel?
500Ω. Two equal resistances in parallel = half.
Can I build up any resistance value?
You can approximate one with series/parallel combinations, but it's usually more practical to look up the nearest E-series standard value — use it alongside the color code decoder / LED resistor calculator.
Standards and sources referenced by this tool
| Item | Value / Formula | Source |
|---|---|---|
| Series | R = ΣRᵢ | Kirchhoff voltage law |
| Parallel | 1/R = Σ(1/Rᵢ) | Kirchhoff current law |
Pure formula calculation, no external API.