What this calculator does
Wheatstone bridge works out unknown resistance from three known resistors at the balance point. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaBalanced when R1/R2 = R3/Rx → Rx = R2·R3/R1
The inputs explained
| Field | What to enter |
|---|---|
| R1 (Ω) | A number, measured in Ω. Starts at 100. |
| R2 (Ω) | A number, measured in Ω. Starts at 150. |
| R3 (variable arm at balance) (Ω) | A number, measured in Ω. Starts at 220. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with r1
Every other input is held at the calculator’s starting values while r1 varies. Select any row to load that scenario into the calculator.