Parallel resistor calculator
Add your resistors, pick parallel or series, and get the equivalent value in engineering notation — k and M suffixes accepted. Need a value your kit does not stock? The pair finder below searches every two-E24 combination. Decode the bands with the resistor color code decoder, or browse the electronics hub.
500 Ω
2 resistors in parallel
| Resistors combined | 1 kΩ ∥ 1 kΩ |
| Smallest individual resistor | 1 kΩ — the parallel total is always below it |
Values accept plain ohms or suffixes: 470, 4.7k, 1M. Blank or unparseable rows are ignored; the total updates as you type.
Hit an exact value
Enter a target resistance and the finder brute-forces the best pair of standard E24 resistors for the current mode — parallel or series — ranked by error, with the most balanced pair winning ties.
| Resistor 1 (E24) | 1 kΩ |
| Resistor 2 (E24) | 1 kΩ |
| In parallel | 500 Ω for a 500 Ω target |
| Error vs target | 0% — exact |
Both suggestions are stock E24 values — but real parts carry 5% tolerance, so measure before committing to a precision stage.
How it works
Parallel resistance adds conductance: 1/R = 1/R1 + 1/R2 + … — for two resistors the shortcut is R = R1 × R2 ÷ (R1 + R2), so two 1 kΩ parts give exactly 500 Ω. Series resistance is the plain sum: R = R1 + R2 + …. The pair finder checks every E24 pair from 1 Ω to 9.1 MΩ (equal values allowed) and keeps the lowest error against your target. Results print in engineering notation — the same k/M suffixes the inputs accept.
Why combine resistors at all
Stock resistor kits come in the E24 series: 24 values per decade, spaced about ten percent apart. That leaves gaps, and circuits do not care about gaps. Say a current-sense stage wants 500 Ω — the kit offers 470 or 510, neither close enough for a tight design. Two 1 kΩ resistors in parallel give exactly 500 Ω, each carrying half the current and dissipating half the power, so two quarter-watt parts do a job that would otherwise need one larger part. Parallel combinations also trim downward in small steps: a 1 MΩ across a 10 kΩ lands at about 9.9 kΩ, a value no kit stocks.
Series works the other direction, adding up. Need 503 Ω? Stack 470 and 33. Both directions are covered above: the calculator sums any list in series or parallel, and the pair finder brute-forces the best two E24 values for a target — the same search you would otherwise run by trial and error at the bench. For the current through the finished combination, the Ohm's law calculator takes the supply voltage and the equivalent resistance directly, and the color code decoder reads the bands on whatever the finder picks. If the two resistors are meant to scale a voltage rather than set a resistance, that is a ratio problem for the voltage divider calculator.
Three warnings. Tolerances do not improve by pairing: two 5% parts in parallel stay within roughly 5%. Power splits in inverse proportion to resistance, so in an unmatched parallel pair the smaller part runs hottest — check it first. And a soldered pair has slightly worse parasitics than a single part, which only matters well above audio frequencies.
Frequently asked questions
What is the formula for resistors in parallel?
Conductances add: 1/R = 1/R1 + 1/R2 + 1/R3 and so on. For the common two-resistor case the shortcut is R = R1 × R2 ÷ (R1 + R2) — product over sum. Two 1 kΩ resistors give exactly 500 Ω; three equal resistors give one third of each.
Why is the parallel total always smaller than the smallest resistor?
Every added resistor is one more path for the current, so the combination conducts better than any single branch. Conductance can only grow when paths are added, which means resistance can only fall. A 10 kΩ in parallel with a 1 MΩ still lands at about 9.9 kΩ — just under the 10 kΩ.
What is 100 Ω in parallel with 100 Ω?
Exactly 50 Ω. Equal resistors in parallel divide by the count: two give half, three give a third, four give a quarter. It is the standard trick for hitting half values and for doubling power handling — two 100 Ω quarter-watt parts share the current and take half a watt together.
Can I mix series and parallel resistors in one circuit?
Yes — work in stages. Reduce each pure series or pure parallel group to its equivalent, then treat that equivalent as a single resistor in the next stage. Two 1 kΩ in parallel (500 Ω) in series with a 470 Ω gives 970 Ω. This calculator handles one stage at a time; run it per group.
Which resistor values can I actually buy?
Standard kits stock the E24 series: 24 values per decade (10, 11, 12, 13, 15, 16, 18, 20, 22, 24, 27 … 91) times powers of ten, at 5% tolerance. Values between those steps are made by combining parts — exactly what the pair finder above searches, restricted to E24 so every suggestion is sourceable.