MotionLab

Strain Calculator

How much a material has stretched or compressed, relative to its original size.

Change in length (m)

Original length (m)

Strain

0.002

ε = ΔL / L (dimensionless)

What you entered

Change in length (m): 0.002Original length (m): 1

1
ε = ΔL ÷ L
0.002 ÷ 1= 0.002

Result

Strain: 0.002

A 0.002m change over 1m original length is a strain of 0.002.

Strain from length change

Strain is the change in length divided by the original length. It is dimensionless, often quoted as a percentage or in microstrain.

Change in length (m)	Original length (m)	Strain	As a percentage
0.0005	0.5	0.001000	0.1%
0.001	1	0.001000	0.1%
0.002	2	0.001000	0.1%
0.01	5	0.002000	0.2%
0.005	1	0.005000	0.5%

The first three rows all give the same strain from different absolute extensions, which is the point: strain is relative, so a 1 mm stretch means something very different on a 0.5 m bar than on a 2 m one. Structural metals typically yield around 0.2% strain, so the fourth row is right at the limit of elastic behaviour for many steels. Engineers often quote microstrain, which is strain times a million - so 0.001 is 1,000 microstrain. Strain is dimensionless, which is why Young's modulus carries the same units as stress.

Strain is dimensionless

Because it's a ratio of two lengths, strain has no units — it's often expressed as a percentage or in microstrain (millionths) for very small deformations, since raw decimal strain values are typically tiny for most structural materials under normal loads.

Strain pairs with stress to describe material behavior

Plotting stress against strain for a material produces a stress-strain curve, which reveals key properties like stiffness (Young's modulus), yield point, and ultimate strength — strain alone is only half the picture.

Frequently asked questions

A 2 m steel rod stretches by 0.5 mm under load. What's the strain?

ε = ΔL/L = 0.0005/2 = 0.00025 = 0.025% = 250 microstrain. This is typical for steel under moderate load — structural steel usually stays below 0.1% strain (1000 microstrain) in normal service.

How much can steel stretch before it breaks?

Mild steel yields at about 0.1-0.2% strain and breaks at 20-30% strain (after extensive necking). Aluminum breaks at 10-15% strain. Rubber can stretch to 500-800% strain. Glass breaks at about 0.1% — almost no stretching before failure.

Is strain always about stretching?

No — strain can be compressive (negative ΔL, squishing) or tensile (positive ΔL, stretching). Shear strain measures angular distortion instead of length change. This calculator handles linear (normal) strain — the most common type in structural problems.

How is strain related to stress and Young's modulus?

They form a trio: σ = E × ε (stress equals Young's modulus times strain). If you know any two, you can find the third. Strain is the measurable deformation, stress is the internal force per area, and E is the material property linking them. See the stress and Young's modulus calculators.