Resistor combination & voltage divider finder

Find the Exact Resistor Combination for Any Target Value

Tell Resistora the resistance or output voltage you need and the resistors you have. It searches every series, parallel, and mixed circuit to find the closest buildable match — plus E-series matching, circuit calculators, and a developer API.

Explore the Tools

Two Ways to Calculate

Use the web tools directly or call the same engines from your code — identical results either way

Web Tools

Six interactive tools: resistor combination finder, E-series matching, voltage divider finder and builder, and circuit calculators. Start solving immediately — no signup, no install.

API & MCP

Call the same engines programmatically with a clean REST API, or connect Resistora to your AI assistant through the built-in MCP server. Consistent JSON, predictable schemas.

Calculation Tools

Six specialized tools for finding, designing, and analyzing resistor circuits

Resistor Combination Finder

Find the resistor combination from your parts bin that matches a target resistance

E-Series Finder

Match a target using standard E6–E192 resistor values you can actually buy

Voltage Divider Finder

Search your resistors for the divider that produces a target output voltage

Voltage Divider Builder

Pick a divider schema and values to calculate the exact output voltage

Circuit Calculator

Calculate total resistance plus combined tolerance, voltage, and power ratings

Series/Parallel Calculator

Quick total resistance for resistors in series or parallel

Built For

From bench hobbyists to professional engineers — Resistora fits wherever you need an exact value

Electrical Engineers

Hit non-standard resistance and voltage targets without trial and error. Find buildable combinations, design dividers, and check tolerance, voltage, and power ratings in one place.

Developers & Integrators

Embed resistor and divider calculations in your apps, design tools, or AI agents via the REST API and MCP server.

Students & Hobbyists

Build the value you need from the parts in your drawer. The free plan covers real projects — no account required to start.

Makers & Repair

Match a target from whatever resistors you have on hand, then open the result in the circuit calculator to verify it before you solder.

Why Resistora

Not just another resistor calculator — it solves the design problem you actually have

Solves the Hard Direction

Most calculators only add up resistors you already picked. Resistora works backwards from your target value to find the combination and circuit topology that gets there.

Always Buildable

Every solution uses only the resistors you supplied, with quantities respected — across series, parallel, and mixed topologies. No substitutions, no ordering, ranked by error.

Consistent Output

Each result returns the same structured data — resistance or output voltage, units, circuit schema, and error percentage — identical whether you use the web UI or the API.

Free to Start, PRO When You Scale

Every tool works for free, no account required. Upgrade for deeper search, custom values, and developer access.

FREE

Start immediately — no registration required

No registration needed
Standard E-series values (up to E96)
2–4 resistors per combination
Top 3 solutions per search
All six web tools, full access
Resistor list saved in your browser

Start Free

Currently Free

PRO

Deeper search, your own values, and developer access

Genetic-algorithm combination engine
Use any custom resistor values
Full E-series depth, up to E192
Top 10 solutions per search
Save up to 100 resistors to your account
REST API + MCP server access

Get PRO Access

API & MCP Access

Run combination search, E-series matching, voltage divider design, and circuit calculations from your own code with a clean REST API — or connect Resistora to your AI assistant through the built-in MCP server. Available on the PRO plan.

View API Documentation

Ready to Get Started?

All tools are available now. No registration needed.

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