Last updated October 10, 2026 · Report an error
A Wheatstone bridge is a classic circuit for precisely measuring an unknown resistance by balancing it against three known resistors until no current flows through a galvanometer connecting the bridge's midpoints.
How it works
Enter the three known resistors (R1, R2, R3), and the calculator applies the balanced-bridge condition Rx = (R2 × R3) / R1 to find the unknown resistance.
- Enter r1 (Ω) — same arm as the unknown resistor.
- Enter r2 (Ω).
- Enter r3 (Ω).
- Click Calculate to see your results.
Examples
Finding an unknown resistor
With R1 = 100 Ω, R2 = 200 Ω, and R3 = 150 Ω, the unknown resistance that balances the bridge is 300 Ω.
Who should use it
- Electronics coursework on bridge circuits and precision measurement.
- Strain gauge and sensor circuit analysis.
Industry applications
- Electronics and instrumentation
- Sensor and measurement systems (e.g. strain gauges, load cells)
Advantages
- Classic, well-established technique for precise resistance measurement.
- Simple formula requiring only three known resistor values.
Limitations
- Requires the bridge to actually be balanced (zero galvanometer current) in the real circuit — this formula alone doesn't confirm that.
Common mistakes to avoid
- Mixing up which resistor is R1 (in the same arm as Rx) versus R2/R3 — this changes which values multiply and which divides.
- Assuming the bridge is already balanced without actually confirming zero galvanometer current in a real circuit.
Best practices
- Double-check your circuit diagram to correctly identify which resistor is in the same arm as the unknown resistance.
- Use precise, well-characterized reference resistors for R1, R2, and R3 to get an accurate result — the bridge's accuracy depends entirely on how well-known these values are.
Tips
- Many real sensors (like strain gauges) work by becoming the "unknown" resistor in a bridge — a small resistance change from strain or temperature shifts the bridge out of balance in a measurable way.
Frequently asked questions
Yes, with no signup and no limit on how many calculations you run.
It means the bridge is adjusted so that no current flows through the galvanometer connecting its two midpoints — at that exact balance point, the ratio of resistors on each side of the bridge is equal, which is what this formula solves for.
A balanced bridge measurement is a comparison against known, precise reference resistors, which historically gave much higher accuracy than direct-reading meters — a technique still used in precision measurement and sensor applications (like strain gauges) today.
R1 sits in the same bridge arm as the unknown resistor Rx — check your specific circuit diagram to identify which position that is, since bridge diagrams can be drawn in different orientations.