Wheatstone Bridge Calculator

How it is calculated

The tool gives the unknown resistance of a bridge that is already balanced, meaning the galvanometer between the two midpoints reads zero. Under that condition the two voltage-divider legs have equal ratios, so Rx = R2 × R3 / R1, with all resistances in ohms (Ω). The result is rounded to two decimals and shown in ohms. The engine needs R1 to be greater than zero, because it is the divisor, and rejects negative R2 or R3; an R2 or R3 of 0 is accepted and gives 0 Ω. It does not calculate the galvanometer current of an unbalanced bridge.

Common mistakes

• Putting the resistors in the wrong positions. The formula divides by R1, so swapping R1 with R2 or R3 gives a different answer; follow the same labelling as your bridge diagram.
• Mixing units, for example R1 in kΩ and R2 in Ω. All three values must be in ohms, since the result is shown in Ω.
• Using the tool before the bridge is truly balanced. If the galvanometer still shows a deflection, the formula does not hold and the answer is only an approximation.
• Entering 0 for R1 (a short circuit in that arm). It is the divisor, so the tool returns no result.