EngineeringFormulaStrain (ε)
Engineering strain is the fractional change in a material's length under load - deformation relative to its original size.
ε = ΔL/L0, a dimensionless ratio (often expressed as a percent or in microstrain). Stress and strain are related through a material's stiffness - its Young's modulus - by σ = Eε within the elastic range.
Because strain is dimensionless, a strain value doesn't by itself say anything about how strong or stiff a material is - a rubber band and a steel rod can experience the exact same strain under very different stresses, since Young's modulus is what actually distinguishes how stiffly each material resists deformation.
Typical Strain by Material/Condition
| Context | Strain | As microstrain |
|---|---|---|
| Structural steel, at yield | 0.001–0.002 | 1,000–2,000 µε |
| Concrete, at crushing | ~0.003 | ~3,000 µε |
| Typical strain-gauge resolution | ~0.000001 | ~1 µε |
| Rubber, elastic range | up to 1.0+ | 1,000,000+ µε |
Used In These Calculators
Related Terms
Frequently Asked Questions
Is engineering strain the same as true strain?
No. Engineering strain (what this site calculates) divides length change by the original length, L0. True strain instead uses the instantaneous length throughout the deformation, which matters at large deformations but is nearly identical to engineering strain for the small, elastic-range strains most structural calculations deal with.
Why is strain expressed in such tiny units like microstrain?
Because real structural strains are genuinely small - a steel beam at working load might strain by a few hundred millionths of its length, values that are awkward to write as a decimal (0.0003) or even a percent (0.03%). Microstrain (millionths) keeps the numbers in a readable range without changing the underlying dimensionless ratio.
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