Wheatstone Bridge Calculator

At balance the two divider ratios are equal, R1 / R2 = R3 / Rx. Rearranged, the unknown resistor is Rx = R2 * R3 / R1. The calculator evaluates that formula directly with the three values you enter.

Two voltage dividers share one supply. R1 over R2 forms the first divider and R3 over the unknown Rx forms the second. A galvanometer or null detector bridges the two midpoints and reads zero when the bridge is balanced.

A balanced bridge has equal voltages at the two midpoints, so no current flows through the detector and it reads zero. When you adjust the known arms until the detector nulls, the ratio condition holds exactly and Rx follows from the three known values.

A bridge compares the unknown against precise reference resistors at a null point, where the eye or meter is most sensitive to a small imbalance. That comparison method can be far more accurate than reading a resistance directly, especially for precise or low-value resistors.

No. At balance the result depends only on the ratio of the resistors, so the supply voltage cancels out and never appears in the formula. That independence is a key reason the bridge is so reliable.

Pick one unit from the menu and use it for all three resistors. Because Rx = R2 * R3 / R1 scales with that unit, entering everything in k ohm gives an answer in k ohm, and the display then reformats it into ohm, k ohm, or M ohm automatically.

The calculator needs positive numbers for R1, R2, and R3. If any field is empty, zero, negative, or non-numeric it shows a prompt to enter positive values instead of a result, since a zero or negative arm has no physical balance point.

The engine computes Rx at full floating-point precision and rounds to nine decimal places, then the display rounds each shown figure to four decimals. For real measurements the accuracy of your reference resistors and detector matters far more than the arithmetic.

Yes. This tool exposes a JSON endpoint that accepts r1, r2, and r3 in ohms and returns rx, so you can script balance calculations. Everything on the page itself runs in your browser with no data sent while you type.