Wheatstone Bridge Calculator
Find the unknown balancing arm, or compute the bridge output voltage.
What it does: Compute the unknown balancing arm of a Wheatstone bridge, or the output voltage when unbalanced.
When to use it: When measuring resistance, building a strain-gauge/sensor bridge, or understanding how a bridge works.
The galvanometer reads 0 when the bridge is balanced? . Fill in below using the convention top-left R1 / bottom-left R3 / top-right R2 / bottom-right Rx.
MEANS —
No history yet. Each calculation is automatically saved to this device.
How to use the Wheatstone bridge calculator
Pick a mode → enter resistances → read Rx or Vout.
- 01
Pick a mode
Find balance: given three arms, compute the fourth arm needed to balance the bridge; Compute output: given all four arms + supply, compute the bridge output voltage.
- 02
Enter resistances
Accepts notations like
1k,4.7k,120. See the bridge diagram below for arm positions. - 03
Read the result
Find balance gives Rx; compute output gives Vout (the sign indicates which side it leans toward).
Bridge arm convention
The labeling this tool uses—the relations swap accordingly if you change the convention.
| Position | Arm | Description |
|---|---|---|
| Left · top | R1 | Top arm of the left divider |
| Left · bottom | R3 | Bottom arm of the left divider, midpoint = Vl |
| Right · top | R2 | Top arm of the right divider |
| Right · bottom | Rx | Bottom arm of the right divider (often the unknown/measured one), midpoint = Vr |
Vout = Vl − Vr; at balance Rx = R2·R3/R1.
Common questions, answered in 3 minutes
What does a "balanced" bridge mean?
The two divider midpoint voltages are equal and the galvanometer reads 0. At this point R1·Rx = R2·R3, independent of the supply voltage—this is exactly why bridge measurements are so accurate.
Why use a bridge instead of measuring the resistance directly?
A bridge turns "measuring an absolute value" into "measuring whether two branches are equal", which is extremely sensitive to tiny changes and unaffected by supply fluctuations. It is widely used with strain gauges and sensors.
What does the sign of Vout mean?
A positive value means the left midpoint potential is higher than the right; a negative value is the opposite. The larger the magnitude, the further from balance.
Are strain-gauge bridges calculated this way too?
The principle is the same, but in practice you must also account for lead resistance, temperature compensation, the excitation source internal resistance and the downstream amplifier input impedance—this tool gives an ideal estimate.
Standards and sources referenced by this tool
| Item | Value / Formula | Source |
|---|---|---|
| Balance condition | Rx = R2·R3 / R1 | Kirchhoff / voltage division |
| Output voltage | Vout = Vl − Vr | Difference of the two divider midpoints |
Ideal bridge model (infinite galvanometer internal resistance), no external API.