Wheatstone Bridge Calculator

What Is a Wheatstone Bridge Calculator?

The Wheatstone Bridge Calculator solves the bridge balance equation for one unknown resistor from the other three. A Wheatstone bridge compares two voltage divider legs, and when the galvanometer reads zero the bridge is balanced. Laboratories use it to measure resistance to high precision.

How the Calculation Works

At balance no current flows through the meter, so the ratios of the two legs are equal:

$$\frac{R_1}{R_2} = \frac{R_3}{R_x}$$

Rearranging for the unknown resistor gives the working formula:

$$R_x = \frac{R_2 R_3}{R_1}$$

Where:

• R1 and R2 form the first divider leg
• R3 and Rx form the second leg
• All four resistances are in ohms (Ω)

Worked Example

With R1 = 6 Ω, R2 = 9 Ω, and R3 = 4 Ω, the balanced value of the unknown resistor is:

$$R_x = \frac{9 \times 4}{6} = 6 \text{ Ω}$$

The calculator can also solve for R1, R2, or R3 when Rx is the known value, which helps when you have a calibrated standard resistor and need to size the rest of the network.

Related free tools

The Wire Resistance Calculator finds resistance from material and geometry, and the Young Modulus Calculator covers strain gauges that often sit inside a bridge.