Enter your Wheatstone Bridge circuit values — input voltage (Vin), and three known resistances (R1, R2, R3) — to calculate either the unknown resistance (R4/Rx) for a balanced bridge or the output voltage (Vout) across the bridge terminals. Choose your calculation method to switch between resistance-finding and voltage-finding modes.
Primary Result
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R1/R2 Ratio
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R3/R4 Ratio
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Bridge Status
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Output Voltage (Vout)
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A Wheatstone bridge is a circuit used to measure an unknown electrical resistance with high precision. It consists of four resistors arranged in a diamond (rhombus) shape connected to an external voltage source and a galvanometer or voltmeter between two midpoints. It was invented by Samuel Hunter Christie and popularized by Charles Wheatstone.
For a balanced Wheatstone bridge, the unknown resistance is calculated as Rx = R3 × (R2 / R1). In this balanced condition, no current flows through the galvanometer. For an unbalanced bridge, the output voltage is Vout = Vin × (R3/(R3+Rx) − R1/(R1+R2)).
Set the bridge to balanced condition by adjusting the known variable resistor until the galvanometer reads zero. Then apply the formula Rx = R3 × (R2 / R1), where R1, R2, and R3 are the three known resistances. This calculator automates that calculation for you.
The Wheatstone bridge principle states that when the ratio of the two pairs of resistors is equal (R1/R2 = R3/Rx), the bridge is balanced and no current flows through the galvanometer. This balanced condition allows the precise determination of the unknown resistor Rx.
Wheatstone bridges are widely used in sensor applications, including strain gauges, pressure sensors, temperature sensors, and load cells. They are valued for their ability to detect very small changes in resistance with high accuracy, making them essential in industrial measurement and instrumentation.
In a perfectly balanced Wheatstone bridge, the output current through the galvanometer (or between the two midpoints) is zero. This null condition is the key feature that makes the Wheatstone bridge so useful for precise resistance measurement.
The equivalent resistance seen by the voltage source is calculated by treating the bridge as two parallel voltage divider branches. For a balanced bridge: Req = (R1+R2) × (R3+Rx) / (R1+R2+R3+Rx). This assumes no current through the galvanometer branch.
Yes. In many sensor applications, the bridge is intentionally operated in an unbalanced state. The output voltage Vout across the bridge terminals reflects the degree of imbalance, which is proportional to the change in the sensing resistor. This voltage can then be amplified and read by a data acquisition system.