The Wheatstone bridge measures resistance very precisely by comparing ratios rather than measuring current. Strain gauges, temperature sensors and load cells all use bridges.
How to use the Wheatstone Bridge Calculator
- Calculate
- R₁
- R₂
- R₃
- R_x
- Supply voltage V_s
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Choose balanced (to find R_x) or unbalanced (to find the bridge voltage). R₁ and R₂ form one arm, R₃ and R_x the other.
Inputs explained
| Field | What to enter |
|---|---|
| Calculate | Choose one: Unknown resistance (balanced), Bridge output voltage |
| R₁ | Units: Ω, kΩ, MΩ, mΩ |
| R₂ | Units: Ω, kΩ, MΩ, mΩ |
| R₃ | Units: Ω, kΩ, MΩ, mΩ |
| R_x | Units: Ω, kΩ, MΩ, mΩ |
| Supply voltage V_s | Units: V, mV, kV, µV, MV |
What each result means
- Unknown resistance R_x = [R₃]×[R₂]÷[R₁]
- Bridge output voltage V_G = [Supply voltage V_s]×([R_x]÷([R₃] + [R_x]) – [R₂]÷([R₁] + [R₂]))
Example values
How the main result changes when R₁ changes and everything else stays at the example values above:
| R₁ (Ω) | Unknown resistance R_x (Ω) |
|---|---|
| 0.5 | 6 |
| 0.75 | 4 |
| 1 | 3 |
| 1.25 | 2.4 |
| 1.5 | 2 |
| 2 | 1.5 |
Formula
Balanced: R_x = R₃·R₂/R₁ · Unbalanced: V_G = V_s·(R_x/(R₃ + R_x) − R₂/(R₁ + R₂))
Worked example
Inputs — Calculate: Unknown resistance (balanced); R₁: 1 Ω; R₂: 2 Ω; R₃: 1.5 Ω.
Results — Unknown resistance R_x = 3 Ω.
Key terms
- Galvanometer
- Sensitive current detector.
Frequently asked questions
What does "balanced" mean?
No current flows through the galvanometer; V_G = 0.
Why is the bridge precise?
It compares ratios, so supply variations cancel.
Where are bridges used?
Strain gauges, RTDs and load cells.
What if V_G is negative?
R_x is smaller than the balance value.