Electronics · Free Calculator
Wheatstone Bridge Calculator
Solve a Wheatstone bridge: find the unknown resistor at balance, or the output voltage of an unbalanced bridge.
Balance conditionOutput voltageStrain gaugeRTD bridge
Unknown R4 at balance100 Ω
Bridge ratio R2/R11
How this result was calculated
- Balance when R1/R2 = R3/R4
- R4 = R3 × R2 ÷ R1 = 100 Ω
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Wheatstone Bridge Equations
Balance: R1 ÷ R2 = R3 ÷ R4, so R4 = R3 × R2 ÷ R1
Output: Vout = Vs × [R4 ÷ (R3 + R4) − R2 ÷ (R1 + R2)]
Output: Vout = Vs × [R4 ÷ (R3 + R4) − R2 ÷ (R1 + R2)]
R1 and R2 form the left divider, R3 and R4 the right divider; Vout is measured between the two midpoints.
Worked example
With 10 V excitation, three 100 Ω arms and R4 = 100.4 Ω: Vout = 10 × (100.4/200.4 − 0.5) = 9.98 mV.
Key insight: a bridge measures a tiny change in resistance as a voltage from zero, which is why strain gauges, load cells and pressure sensors are almost always bridges.
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Frequently Asked Questions
What is the balance condition of a Wheatstone bridge?
The ratio of the arms on each side must be equal: R1/R2 = R3/R4. The output is then zero.
Why is a load cell output given in mV/V?
The bridge output is proportional to excitation, so mV/V describes the sensor independently of the supply voltage.
Is the bridge output linear?
Only approximately, for small changes. A quarter bridge has a small nonlinearity that grows with strain.
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