Strain Calculator

Quick answer

Engineering strain ε = ΔL ÷ L. Stretching a 1,000 mm member by 0.5 mm gives a strain of 0.0005, or 0.05%, which is 500 microstrain (µε).

Enter the change in length and the original length. The calculator returns strain as a ratio, a percentage and in microstrain.

Related tools: Moment of Inertia Calculator: Area moment of inertia of common cross-sections.

How to use the Strain Calculator

1. Enter change in length.
2. Enter original length (above 0).
3. Press Calculate to see the result, and use Reset to start again.

Formula and method

Use the same unit for both lengths.

Worked examples

These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.

The first line is the headline result (strain). Below it the strain Calculator lists percent and microstrain, which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.

Reading strain

Strain is dimensionless. Steel yields at about 0.2% strain (2,000 µε), so 500 µε is well within the elastic range. With a modulus of 200 GPa, 500 µε corresponds to a stress of 100 MPa.

Engineering versus true strain

This is engineering strain, based on the original length. For large deformations, true strain uses the natural logarithm of the length ratio. The two agree closely for small strains.

How the result changes with change in length

Holding every other input at the first worked example, this table changes only change in length. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.

What happens with invalid input

These messages are produced by the calculator itself, so you know what to fix.

• Change in length: left empty shows "Enter change in length." beside that field and no result.
• Original length: entering "0" shows "Original length must be greater than 0." beside that field and no result.

Choosing between the Strain Calculator and similar calculators

Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.

Background: structural and wiring estimates

Structural and electrical results are only as good as their assumptions. Bending stress is the bending moment divided by the section modulus, and an allowable stress is the yield strength divided by a safety factor that depends on the governing design code and the type of load. For a single-phase or DC run the voltage drop uses the round-trip length: V = 2 × L × R per unit length × I.

Recommended limits, such as keeping branch-circuit voltage drop around 3%, differ between sources and code editions. These pages are estimates: follow the applicable code and a qualified engineer or electrician for real work.

Assumptions and limitations

• Engineering (not true) strain

Use results as engineering estimates and check them against the governing standards, safety factors and a qualified engineer's judgement before relying on them.

If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for change in length and original length to confirm this.

Related calculators

• Moment of Inertia Calculator — Area moment of inertia of common cross-sections.
• Stress Calculator — Normal or shear stress from force and area.

Sources

• OpenStax, University Physics Volume 1 (Rice University): mechanics

Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.