Wheatstone Bridge Calculator

What is a Wheatstone Bridge?

A Wheatstone bridge is a circuit with four resistors arranged in a diamond configuration with a voltage source and a galvanometer (null detector). When balanced, the galvanometer reads zero and the unknown resistance can be calculated precisely. It's the foundation of highly accurate resistance measurement.

The Balance Condition Formula

When the bridge is balanced (galvanometer = 0):

R_x = (R2 × R3) / R1

Or equivalently: R1/R2 = R3/R_x

How to Use This Calculator

Enter R1, R2, and R3 (the known resistors). The calculator finds the unknown R4 at balance. You can also enter all four resistors to calculate the bridge output voltage when slightly unbalanced — the principle behind strain gauges and load cells.

Practical Examples

Example 1: R1 = 100Ω, R2 = 200Ω, R3 = 150Ω. R_x = (200 × 150) / 100 = 300Ω.

Example 2: Strain gauge bridge: four 120Ω strain gauges. Under load, one gauge changes to 120.5Ω. Output voltage at 10V excitation ≈ 0.5 / (4 × 120) × 10V = 10.4 mV — detectable with a precision amplifier.

Applications

Wheatstone bridges are used in: precision resistance measurement, strain gauge load cells (weight scales, force sensors), RTD temperature sensing circuits, pressure transducers, and bridge-type signal conditioners for instrumentation.