Strain Gauge Calculator (ΔR and Bridge Output)
By Santaji GadepatilinUpdated October 28, 2026
A strain gauge is a fine foil grid whose resistance changes slightly when it is stretched or compressed. Wired into a Wheatstone bridge, it measures force, pressure and weight in load cells and transmitters. This strain gauge calculator gives the resistance change and bridge output — see the strain gauge working principle and bonded vs unbonded strain gauges.
How to use the strain gauge calculator
Enter the gauge resistance, gauge factor, strain in microstrain, bridge excitation and choose the bridge configuration. You get the resistance change per gauge, the bridge output and its sensitivity in mV/V.
Strain gauge formulas
ΔR = R × GF × ε · Vout ≈ Vex × N × GF × ε ÷ 4
where N is the number of active arms (1, 2 or 4). The quarter-bridge result is slightly non-linear at large strains — see the Wheatstone bridge calculator for the exact value.
Output at 10 V excitation, GF = 2
| Strain | ΔR (350 Ω gauge) | Quarter bridge | Full bridge |
|---|---|---|---|
| 10 µε | 7.0 mΩ | 0.05 mV | 0.20 mV |
| 100 µε | 70.0 mΩ | 0.50 mV | 2.00 mV |
| 500 µε | 350.0 mΩ | 2.50 mV | 10.00 mV |
| 1000 µε | 700.0 mΩ | 5.00 mV | 20.00 mV |
| 2000 µε | 1400.0 mΩ | 10.00 mV | 40.00 mV |
From strain to stress
For steel (E ≈ 200 GPa), stress = E × ε: 1,000 µε corresponds to about 200 MPa.
Load cells
Load cells are rated in mV/V at full load — commonly 2 mV/V. With 10 V excitation, a 2 mV/V cell gives 20 mV at full capacity. Amplify it with an instrumentation amplifier.
Frequently asked questions
What is the gauge factor?
The ratio of relative resistance change to strain, GF = (ΔR/R) ÷ ε. Metal foil gauges have GF ≈ 2; semiconductor gauges can exceed 100.
What is a microstrain?
One millionth of a unit of strain (10⁻⁶ m/m). Steel at its typical working stress sees about 500–1,500 µε.
How big is the output of a strain gauge bridge?
Very small: a quarter bridge with GF 2 at 1,000 µε gives about 0.5 mV/V — 5 mV with 10 V excitation — so an instrumentation amplifier is needed.
Why use a full bridge?
It gives four times the output of a quarter bridge and cancels temperature effects and lead resistance, which is why load cells use full bridges.