Wheatstone Bridge Input Form
Use one consistent resistance unit throughout the calculation. For solve modes, enter the known resistors and optionally compare against an actual measured arm.
Formula Used
Bridge balance condition: R1 / R2 = R3 / R4
Solve unknown R4: R4 = (R2 × R3) / R1
Solve unknown R3: R3 = (R1 × R4) / R2
Left midpoint voltage: VL = VS × R3 / (R1 + R3)
Right midpoint voltage: VR = VS × R4 / (R2 + R4)
Bridge output voltage: VOUT = VL − VR
Equivalent bridge resistance: REQ = ((R1 + R3)(R2 + R4)) / (R1 + R2 + R3 + R4)
Output Thevenin resistance: (R1 || R3) + (R2 || R4)
These equations assume ideal resistors, a stable excitation source, and a standard Wheatstone bridge topology with the output measured between the midpoint nodes.
How to Use This Calculator
- Select the calculation objective that matches your bridge task.
- Enter the excitation voltage and choose one consistent resistance unit.
- Fill in the known resistor arms. Leave the solved arm for interpretation only.
- Set a balance tolerance if you want the result labeled balanced or unbalanced.
- Choose decimal places for cleaner engineering output.
- Press the calculate button to show the result above the form.
- Download the result as CSV for spreadsheets or PDF for reports.
Example Data Table
| Case | R1 | R2 | R3 | R4 | VS | Expected Output | Notes |
|---|---|---|---|---|---|---|---|
| Balanced bridge | 120 Ω | 100 Ω | 180 Ω | 150 Ω | 10 V | 0.0000 V | Exact ratio match. Bridge output is zero. |
| Slight unbalance | 120 Ω | 100 Ω | 180 Ω | 147 Ω | 10 V | 0.0486 V | Useful for sensitivity and mismatch checks. |
| Unknown arm target | 470 Ω | 330 Ω | 1000 Ω | ? | 5 V | R4 = 702.1277 Ω | Use solve R4 mode for this setup. |
Frequently Asked Questions
1. What does a Wheatstone bridge calculator measure?
It solves unknown resistance, checks balance, estimates output voltage, and reports currents, sensitivity, power, and equivalent resistance for a standard bridge network.
2. When is the bridge considered balanced?
The bridge is balanced when the resistor ratios satisfy R1 / R2 = R3 / R4. Under that condition, the midpoint voltages match and the differential output ideally becomes zero.
3. Why is my output voltage not zero?
Any ratio mismatch, resistor tolerance, supply variation, or rounding difference shifts the midpoint voltages. That creates a nonzero differential output and indicates an unbalanced bridge.
4. Can I use kilo-ohms or mega-ohms here?
Yes. Use one consistent unit across all resistor inputs. The calculator treats the values proportionally, so mixing units within one calculation would distort the result.
5. What does sensitivity in mV/V mean?
It shows bridge output voltage normalized to excitation voltage. This is common in sensor systems because it compares output strength without depending on one specific source voltage.
6. Why does tolerance matter in bridge analysis?
Tolerance sets how close an actual resistor must be to the theoretical balanced value before the result is labeled balanced. This helps practical engineering checks with real components.
7. Can this calculator help with sensor bridge circuits?
Yes. It is useful for strain gauges, load cells, RTD networks, and other resistive sensors that use bridge imbalance to convert small resistance changes into measurable voltage shifts.
8. What is output Thevenin resistance?
It is the effective resistance seen across the output nodes when the source is shorted. It helps estimate loading effects when an amplifier or measuring instrument is connected.