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Elongation: Definition, How To Calculate, and Importance

Learn more about this type of measurement and what it means in manufacturing.

Xomety X
By Team Xometry
March 16, 2023
 10 min read
Desing Reference Poster: Sheet Material Selection Guide
March 28, 2023

Elongation is the measurable tendency of a material to stretch when under strain. Engineers use a standardized testing procedure and a dumbbell-shaped test sample to evaluate a given material’s characteristic elongation behavior. The sample’s elongation is expressed as a percentage — its increase in length is divided by the original length and multiplied by 100 to calculate this value. 

Elongation is important because it is a measure of a material’s ductility — its ability to deform without breaking. This is a key measure in 3D-printable materials, as it is relevant to the practical durability of 3D-printed components in real-world applications. This article will define elongation, its importance, and how to calculate it.

What Does Elongation Mean?

Elongation is the amount that a material permanently lengthens when experiencing a tensile force (strain). It is a numerical measure of the ductility of the material — how easily it deforms under strain. It is measured according to very specific controlled conditions so that the values of elongation can be quantitatively compared between materials.

Elongation is specifically measured using a standardized shape of sample material, which is then acted upon by a known pulling force. The length by which the material sample lengthens is measured until the force is great enough to break the sample.

What Is Elongation in the Physics of Deformation?

Elongation in terms of the physics of deformation is a measure of how much an element lengthens when subjected to tensile stress. It’s expressed as a ratio of the new length to its original length.

What Is Elongation in Astronomy?

Elongation in astronomy is a measure of the angular separation between a body in the solar system and the sun when viewed from earth. It describes the relative position of planets and other celestial bodies in the solar system, compared to the earth and sun.

What Is Elongation in Geometry?

Elongation in geometry refers to the stretching of a geometric shape along one or more axes. For example, in a 2-dimensional plane, if a square were to be elongated along one axis, it would become a rectangle. In a 3-dimensional space, if a cube were elongated along a single axis, it would become a rectangular prism. This concept is important in geometric transformations.

What Is Elongation in Plasma Physics?

Elongation in plasma physics refers to the shape of a fusion plasma. A plasma cloud can be shaped, and the elongation of a particular shape is defined as the ratio of the length of the cloud on its longest axis to the length of its shortest axis. Elongation is an important factor as more elongated plasma clouds tend to be less stable and more difficult to confine.

What Is Elongation in Biology?

Elongation in biology is a part of the DNA translation process, where proteins are built from RNA that has been transcribed from DNA. More specifically, elongation is the second phase of translation, occurring between the initiation and termination of the process. Elongation refers to the amino acid chain lengthening during translation.

How To Calculate the Elongation of a Material?

The elongation of a material is calculated according to international testing standards. The most common standard for calculating elongation is ASTM D412. It specifies the shape of the material sample to be used. The shape is called a dumbbell, as it is roughly oblong but with wider ends (for gripping) and a thinner strip in the middle, which will elongate when pulled.

The material sample is gripped by a testing machine and a steadily increasing pulling force (strain) is applied to the dumbbell. The testing machine measures how the sample length increases with increasing strain. This data is plotted onto a graph. The elongation is calculated as the amount that the material’s length increased, divided by its original length. This is quoted as a percentage. 

What Is the Formula of Elongation?

The formula for elongation is the deformation (increase in length) of a sample divided by the original length of the sample, multiplied by 100 (to convert to a percentage).

Percent Elongation = 100 x ((Final Length - Original Length) / Original Length)

Or, written using symbols: 

Percent Elongation = ɛ = (ΔL/L) x 100

What Is the Unit of Elongation?

Elongation is reported as a percent, so it doesn’t technically have a unit. This is because the elongation of a material is a ratio of the material’s change in length when it breaks to the original length of the sample. The ratio is converted to a percentage.

What Is the Symbol for Elongation?

The symbol for elongation is the lowercase Greek letter ε (epsilon). 

What Is the Importance of Elongation?

Knowledge of elongation is important so you can understand how much a material will deform under strain. It can be used as a measure of ductility. The deformation and ductility of a material are important to know for applications where some deformation is expected, such as in crash barriers. Conversely, elongation is an important factor when designing parts such as door hinges which can accept very little deformation under strain.

What Is Elongation in 3D Printing?

Elongation in 3D printing is the amount of deformation that a 3D-printed material can withstand before breaking. It is an indication of how durable a 3D-printed item will be. The growing popularity of 3D printing has underscored the poor mechanical strength of many printable materials and technologies (such as FDM or resin).

Is Elongation an Important Measure in 3D Printing Materials?

Yes, elongation is an important consideration when choosing 3D printing materials, as it provides information about how much the material can deform without breaking. The physical properties of their constituent materials dictate the usefulness of 3D-printed components. Many items must be durable in order to be practical in real-world circumstances. 

Is There a Device Used in Measuring the Elongation of Materials?

Yes, there are specially designed devices for measuring the elongation of materials according to international standards like ASTM D412. These testing systems have a number of components, each of which is intended for certain material tests. 

Firstly, the device has grips that hold each end of the material dumbbell sample. Secondly, the testing system uses a measuring device called an extensometer to measure the change in the sample’s length as increasing strain is applied. It is also possible to use machines that include environmental chambers. By encasing the grips, material sample, and extensometer, they control the environmental conditions (such as temperature) in order to test under very specific conditions.

A number of specialist suppliers manufacture these testing systems for sale to any organization that needs to carry out regular tests according to standards such as ASTM D412.

What Are the Different Types of Elongation Measurement?

The different types of elongation measurements are as follows: 

1. Ductility

Ductility is the ability of a material to deform without breaking. Materials that are not ductile are instead called brittle — they deform very little before breaking. The ductility of a material can be inferred by a number of measurements — the most common is percent elongation, but the reduction in area and cupping tests can also be important.

2. Elongation at Break

Elongation at break is the measured elongation of a sample of material at the point at which it breaks. Tensile stress is applied to the material sample, causing it to lengthen. As this stress increases, the stretching of the material will first be elastic (can revert to its original position when the stress is released) and then plastic (permanent deformation). If the stress continues to be applied after plastic lengthening occurs, the material will eventually break. The length at this point is the elongation at break, often stated as a percentage lengthening compared to the original length.

What Is Percent Elongation?

Percent elongation is the percentage that a material stretches beyond its original length before it actually breaks. Elongation is measured as the change in length in a material sample, divided by its original length, multiplied by 100 to convert it to a percentage.

How To Calculate the Percent Elongation?

Percent elongation is calculated using data from a testing system. First, the material to be tested is cast or machined into a specific dumbbell shape according to the international standard ASTM D412.

Second, the dumbbell of material is clamped into the testing machine and a tensile (stretching) force is applied. An extensometer measures the increase in length within the thin section of the dumbbell. This relationship between length and tensile strength can be plotted on a simple graph. The test ends when the dumbbell breaks.

Finally, percent elongation is calculated from this data. The change in total length divided by the starting length multiplied by 100 gives the percent elongation. 

Why Do We Need To Calculate Material Elongation?

It is valuable to calculate material elongation so that there is a standardized way to estimate and compare the ductility of different materials. It is important to be able to quantitatively compare different grades on a number of material properties, especially when selecting a specific grade of material for a project. The elongation of a material can be a critical property in certain applications such as crash barriers that need to absorb significant energy before failing.

How Does Tensile Strength Relate to Elongation?

The relationship between tensile strength and elongation depends on the material. Typically, materials that have high tensile strength tend not to elongate by much — these are materials like ceramics and some tough metals. This means that they will withstand high tensile stress before breaking; however, since they’re brittle, they won’t deform much before that breaking point. That can make the break seem sudden or unexpected. 

Typically, materials with high elongation values have low tensile strengths. If the material is easily stretched, it often cannot withstand much tensile stress. This includes most polymers plus soft metals like copper. However, there are engineered materials (alloys and composites) that exhibit significant elongation in combination with high tensile strength. These are valuable for specific applications such as structural components that experience high dynamic loads.

What Is the Difference Between Elongation and Tensile Strength?

Tensile strength indicates how much force the material can withstand, whereas elongation indicates how ductile the material is. Tensile strength is a measure of how much tensile stress (force) can be exerted on a material before it breaks. It is measured in units of force per unit area, such as psi or MPa. Elongation is rather a measure of how much that material will stretch under tensile stress before breaking — its so-called ultimate elongation. It is measured as a percentage change in the sample’s length.


This article presented elongation, explained what it is, and discussed why it's important to calculate. To learn more about elongation, contact a Xometry representative.

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Xomety X
Team Xometry
This article was written by various Xometry contributors. Xometry is a leading resource on manufacturing with CNC machining, sheet metal fabrication, 3D printing, injection molding, urethane casting, and more.