Strain Calculator
Compute engineering strain from an original length and its change.
Formula
ε = ΔL / L
Inputs
- Original length (mm)
- Change in length (mm)
What it does
Engineering strain is the change in length divided by the original length: ε = ΔL / L.
Where it's used
Tensile tests, strain gauges and thermal expansion checks.
How to use it
- Enter the original length.
- Enter the change in length (same units).
- Read the strain.
The formula explained
- ε
- strain — no units
- ΔL
- change in length
- L
- original length
Worked example
A 2 m bar stretched by 1.2 mm.
Inputs:
- Original length: 2000 mm
- Change in length: 1.2 mm
The calculator gives:
- Result: 0.06 %
- Strain (dimensionless): 0.0006
- Microstrain (µε): 600
Tips and common mistakes
- Strain is often quoted in microstrain (µε = 10⁻⁶).
- In the elastic range, stress = E × strain (steel E ≈ 200 GPa).
- Both lengths must use the same unit.
Questions people ask
How do I get the stress from the strain?
In the elastic range σ = E × ε. For steel (E ≈ 200 GPa) the example strain of 0.0006 means about 120 MPa.
How is strain measured?
With strain gauges bonded to the part. Their resistance changes by the gauge factor (about 2) times the strain: at 600 µε a 350 Ω gauge changes by about 0.42 Ω, read with a Wheatstone bridge.
When does a material stop springing back?
Above its yield point. Mild steel yields at about 250 MPa, which is roughly 1 250 µε; beyond that, part of the stretch remains when the load is removed.
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Enter your values to get the result with the formula, substituted values and an explanation of each step.