Resistor Combination Finder

What Is the Resistor Combination Finder?

The Resistor Combination Finder searches your parts bin for the best series, parallel, or mixed resistor circuit that matches a target resistance. Instead of guessing which combination of resistors to reach a value, you enter the resistors you own, set a target, and the tool evaluates every valid circuit topology across 2, 3, and 4 resistors — returning the closest achievable results ranked by error.

The result is always immediately buildable: every solution uses only resistors from your supplied list, with quantities respected. No ordering, no substitutions, no spreadsheets.

Why Finding the Right Combination Is Hard

Resistors come in discrete standard values. Even a well-stocked parts bin rarely contains the exact resistance you need, so combining two or more resistors in series or parallel is a common workaround. The problem is the search space: with 10 resistors and circuits of up to 4 components, there are thousands of candidate combinations once you account for different topologies — series, parallel, and mixed arrangements.

Doing this by hand means computing each combination, checking each topology, and tracking the best error — work that takes minutes per candidate and hours for a thorough search. This tool completes the entire search in seconds.

Circuit Topologies Covered

The finder evaluates 16 distinct circuit schemas across 2, 3, and 4 resistors:

1. 2-resistor circuits: series and parallel.
2. 3-resistor circuits: all-series, all-parallel, two in series with one in parallel, and two in parallel with one in series.
3. 4-resistor circuits: all-series, all-parallel and mixed topologies combining series and parallel sub-groups in different arrangements.

Every schema is checked against every valid combination of your available resistors, giving the algorithm full visibility into what your parts bin can achieve.

How to Use the Resistor Combination Finder

1. Add your resistors. On the Resistors tab, add the resistance values available in your parts bin. FREE users pick from the default standard value list; PRO users can type any resistance directly.
2. Open Settings and enter your target. Click the Settings button, then type the resistance you want to achieve and set the minimum and maximum number of resistors the circuit may use.
3. Run the search. Click Start. The algorithm evaluates all topologies across all valid resistor combinations and returns the top solutions ranked by closeness to your target.
4. Browse solutions. The Solutions tab shows the achieved resistance, error, and a schematic of the circuit. Navigate through results and pick the one that best fits your accuracy and component count requirements.
5. Open in Circuit Calculator. Use the Edit button on any solution to open it in the Circuit Calculator with the schema and resistor values pre-populated, where you can adjust values and recalculate freely.

Free vs PRO

On the free plan, the finder looks up combinations from precomputed standard-value tables and returns the top 3 results. You pick resistors from the default standard-value list, and your list is stored locally in your browser — no account needed.

PRO swaps the table lookup for a genetic-algorithm search that accepts any custom resistor values, returns the top 10 results, and lets you save up to 100 resistors to your account. Both plans search circuits of 2–4 resistors across the full set of series, parallel, and mixed topologies.

Frequently Asked Questions

How does the Resistor Combination Finder work?

You enter the resistors you have (values and quantities) and a target resistance. The finder evaluates every valid series, parallel, and mixed circuit across 2 to 4 resistors and returns the combinations that come closest to your target, ranked by error percentage.

Do the results only use resistors I actually own?

Yes. Every solution is built exclusively from the resistors you supplied, and the available quantity of each value is respected — so each result is immediately buildable with no substitutions or ordering.

How many resistors can a combination use?

Combinations use 2 to 4 resistors on both the free and PRO plans. More resistors widen the search space and let you hit tighter targets at the cost of a larger circuit.

What is the difference between the free and PRO plans?

The free plan looks up combinations from precomputed standard-value tables and returns the top 3 results, with your resistor list stored in your browser. PRO runs a genetic-algorithm search over any custom resistor values you enter, returns the top 10 results, and lets you save up to 100 resistors to your account.

Can I refine a solution after finding it?

Yes. Use the Edit button on any solution to open it in the Circuit Calculator with the schema and resistor values pre-filled, where you can adjust values and recalculate freely.