Wheatstone Bridge Calculator
Enter the three known resistors of a Wheatstone bridge to find the unknown resistor Rx at balance. The bridge balances when the two divider ratios match, so R1 over R2 equals R3 over Rx and Rx works out to R2 times R3 over R1.
How to use the Wheatstone bridge calculator
- Enter resistor R1 in ohms (the top of the first divider).
- Enter resistor R2 in ohms (the bottom of the first divider).
- Enter resistor R3 in ohms (the top of the second divider).
- Read the unknown resistor Rx that balances the bridge.
Examples
R1 100, R2 200, R3 150
r1 = 100, r2 = 200, r3 = 150
Rx = 200 * 150 / 100 = 300 ohms
All resistors equal
r1 = 1000, r2 = 1000, r3 = 1000
Rx = 1000 ohms
Frequently asked questions
What is the Wheatstone bridge balance equation?
At balance the two divider ratios are equal, R1 / R2 = R3 / Rx. Rearranged, the unknown resistor is Rx = R2 * R3 / R1.
How is the bridge arranged?
Two voltage dividers share one supply. R1 and R2 form the first divider, while R3 and the unknown Rx form the second. A galvanometer connects the two midpoints.
What does a balanced bridge mean?
A balanced bridge has equal voltages at the two midpoints, so no current flows through the detector and it reads zero. The ratio condition above then holds exactly.
Why use a Wheatstone bridge instead of an ohmmeter?
A bridge compares the unknown against precise reference resistors at the null point, which is very sensitive and accurate. It does not depend on the exact supply voltage.
Does the supply voltage affect Rx?
No. At balance the result depends only on the ratio of the resistors, so the supply voltage cancels out and does not appear in the formula.
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