Measurement Tools

Goniometer With Definition, Parts, Types, Uses And Reading

We explain that what are the parts of goniometer with types and images to better learn the tool. Lets Read Physics…

What is a goniometer?

A goniometer is an instrument that measures an angle or allows an object to rotate to a precise angular position. It has a 180 ° or 360 ° graduated circle, it has a built-in rotating surface on its axis of symmetry, so that it can measure any type of angular value.

The rotating surface has a built-in vernier for precise angle measurement.

The term goniometry is derived from two Greek words.

  • gōnia, angle of meaning.
  • metron, measure of meaning.

This instrument to measure angles is particularly used in the study of crystals. Nicolaus Steno in 1669 determined the inter-facial angles of quartz crystals by cutting sections perpendicular to the edges, the plane angles of the sections were the angles between the faces that were perpendicular to the sections.

The first instrument used to measure these angles was the contact goniometer devised by Arnould Carangeot in 1780.


What is a goniometer for?

A goniometer is used to measure angles in different industrial and scientific areas, although it is also used in medicine to calculate the angles reached by the joints.

It is mainly used in the fields of architecture for the elaboration of plans, as well as in topography, in the calculation of latitudes and military calculations, in crystallography and in the area of ​​communication and broadcasting.

The areas where its use is most frequent are:

  • Topography
  • Military calculations
  • Communication and Broadcasting
  • Crystallography
  • Architecture (blueprint design)
  • Calculation of latitudes
  • General carpentry work
  • Pipe fittings
  • Installation of window and door frames
  • Cabinet and shelf installations
  • Decoration of exterior and interior spaces

How to use it?

For the correct reading of the goniometer, it is necessary to know how to use the vernier scale, which offers a second scale for greater precision of the result.

The value of the main scale is indicated in degrees starting at 0 and then another line must be identified that matches the second value, which is in minutes.

The combination of both values ​​provides the numerical result.

To make the measurement , the ruler is placed on the end that best suits the angle to be measured. The goniometer support is then supported at the adjacent angle of the goniometer.

The nuts are loosened so that the mobile arm slides well and the value of the desired angle is read.

It is necessary to make sure that it is in perfect condition, to avoid any problem at the time of measurement.

Important point to use goniometer

  • Take the goniometer with caution.
  • Look and move the goniometer to see that it works perfectly.
  • Determine the object to which the angle will be measured.
  • After you have selected the object, carefully place the goniometer.
  • You should make sure that it has a suitable inclination and that it is adjusted with the sides of the object that you will measure.
  • Observe the graduation that the goniometer has.
  • After you know the graduation of the goniometer, you have to identify a black line that coincides with the arm of the goniometer that has the flange.
  • Finally, you must proceed to take these readings.

Benefits of using a goniometer

In the world there are objects with numerous shapes and a tool is needed for their respective measurement, this instrument is generally used in industries to provide an exact measurement on their products or their manufacture.

Without the goniometer in action it is difficult to provide exact data to be able to create or join different objects.

  • The goniometer is easy to take anywhere
  • Its construction materials are of good quality
  • Your measurements you provide are accurate


goniometer has specific characteristics that, although used by various sciences, do not vary, it has a measuring range in 360 ° angles, it is made of stainless steel or plastic, it has a fine adjustment and a vernier magnifying glass.

It is usually made of stainless steel, but there are also some made of plastic. It is an easy to use instrument.

A goniometer consists of three parts: a body a stationary arm a mobile arm.

  • Body : similar in design to a traditional conveyor. It can be 180 and 360 °.
  • Stationary arm : attached to the body of the goniometer, so its movement is dependent on it.
  • Movable arm : generally, it is independent of the body and its position is moved and fixed with an element similar to a screw, when making the measurement.


All varieties of goniometer have the same principle of operation, let’s see:

The vernier,  which goes on the rotating disk, has a scale graduated both to the right and to the left, which allows measurements to be made both in a clockwise and anti-clockwise direction.

It should be noted that the resolution or appreciation of this type of goniometer is 5 min of arc, which is shown numerically later.

In the center of the goniometer there is a screw that serves both as the axis of rotation and fixer of the angular position. Some precision goniometers have an additional wheel, to control the fine turn, so that it can be adjusted more precisely to the piece to be measured.

Said piece is placed between the variable rule and the fixed rule or square. Both the goniometer and the part already positioned are candled to ensure a perfect fit.

Once any passage of light between the piece and the reference surface of the ruler or square has disappeared, the position is fixed with the articulation fixator or fixing screw. Finally, the measurement is carried out, the steps of which are detailed below:

Parts of a goniometer in detail

This instrument is mainly composed of a semi-circle graduated with 180º or a circle with 360º. There is a great variety of goniometers, some only have a graduated circle, others have a graduated ruler to measure distances, they can also have a rotating dial in which a vernier is inserted to take measurements with greater precision.

Parts of a goniometer

  • Graduated disk
  • Magnified lens
  • Squad
  • Squad extension
  • Interchangeable strips
  • Fixing screws
  • Fine adjustment screw

Parts of a goniometer

How is the goniometer used?

To use the goniometer, the object whose angle of inclination is to be measured is wedged between the sheet and the disk of the goniometer, as shown in figure 4. There the angle to be measured has been marked in fuchsia.

How is the goniometer usedHow to measure an angle with a basic goniometer

Green and blue parallels have been drawn over the image to guide the reader. The fuchsia angle is opposite the yellow angle at the vertex. When you have opposite angles through the vertex, they measure the same.

The angle in yellow measures the same as the orange, since they are between the green and blue lines, which are parallel. Once convinced of this, the reading is made immediately by observing the indicator on the sheet.

The angle of the piece to be measured is an acute angle and the reading is made from left to right. In the enlarged image they read 48º.

Enlarged view of the measure
Enlarged view of the measure

Of course, readings can be done from right to left, as there is a double scale for that. Doing it one way or the other depends on the object to be measured.

Appreciation error

All measuring instruments have an appreciation, which is the smallest division of the scale, and any measurement made, whether with the goniometer or any other, will always be affected by error.

For example, in the simple goniometer we have just seen, the smallest division corresponds to 1º.

The maximum error that can be made in a measurement made with this goniometer is more or less appreciation. According to this, the reading of the example is expressed as:

L = 48 ± 1º

In general, the appreciation of a scale like this is calculated by selecting two arbitrary readings, and counting the number of divisions between them, like this:

Appreciation = Major Reading – minor reading / number of divisions.

How to read a goniometer

To read the goniometer correctly, it is necessary to know the use of the vernier scale, which establishes a second scale so that the reader can more accurately identify the result.

The zero indicates the value of the main scale (which is in degrees) and another line must be found to match the second value (which is in minutes). From the combination of both, the numerical result will be obtained.

Goniometer in minutes

Readings with the precision goniometer

The precision goniometer has a vernier : a second scale placed on a movable disk and that can be moved below the main scale. The vernier allows for finer readings.

As always, the measurement made with the main scale results in degrees and can be done clockwise (from left to right) or counterclockwise (from right to left), depending on convenience.

The reading on the main scale is carried out with the procedure described in the previous section. The 0 of the vernier acts as an indicator in this case.

Now we go to the final reading with the vernier, which will give us the minutes. Each division is equivalent to 5 ‘(angular minutes) and can also be read from left to right or right to left.

To find the measurement, the line of the vernier must be selected that best coincides with any of the lines on the fixed scale, and that will be the fraction in degrees that must be added to have the complete reading.

Reading example 1

As an example, let’s see the reading of the figure, done counterclockwise. The 0 of the vernier indicates 64º (green line).

Readings with the precision goniometer
Example of reading from right to left.

Now let’s look at the line of the vernier that best matches one of the main lines. In the figure it has been highlighted in fuchsia. It coincides with division number 30 on the vernier scale. So our angle measures:

1 = 64º 30 ‘= 64.5º

As for the appreciation of this goniometer, it depends not only on the main scale, but on the vernier. Goniometers usually have 12 or 24 division verniers in each half. The one in the example has 12.

It is calculated as follows:

Appreciation = least division of the main rule / number of divisions of the vernier

In this case, the smallest division is 1º = 60 ´, and the divisions are 12:

Appreciation = 60´ / 12 = 5´

Therefore the reading is reported in this way:

1 = 64º (30 ± 5) ´

Reading example 2

Now let’s try a clockwise reading.

Readings with the precision goniometerGoniometer reading taken from left to right.

The 0 of the vernier coincides with 42º (orange color), while the division of the vernier that best coincides with any of the divisions on the main scale (turquoise blue color) corresponds to 20´. Therefore the measured angle is:

2 = 42º (20 ± 5) ´

The reader may wonder what happens if no division matches exactly. When the 0 of the vernier is in the middle of two main divisions, the division closest to 0 is taken as the degree reading. The rest of the measurement is done as already described

It is always up to the person making the measurement to select the divisions that best match. Two people taking the same measurement may disagree, but almost always on the fine measurement.

Types of goniometers

There are different types as they have a variety of applications in industry and science.


It is the best known type since it is the most common within its type.


With vernier scale

This type is characterized by having 1 smaller scale integrated in the rotating disk, this goniometer is used to make measurements with greater precision.

vernier scale

Universal square

It is characterized by being a graduated ruler with a set of extra heads (square head, centering head and a protractor). When the ruler is used in conjunction with the protractor, it acts as a goniometer.

Universal square


This goniometer being digital, no parts are omitted, it has the same characteristics, fixing screws, strip, square. The only element that changes is the scale graduated by a small screen that indicates the measurement.


Multifunctional digital

This instrument is characterized by having different functions included. Like those of a level and a goniometer.

Multifunctional digital 


It is used when a precision tightening of screws is required. Some manufacturers, such as automotive or machinery, specify the tightening of screws at angles.


With torque meter

It is used to make an angle tighten to tighten the motor head bolts.

torque meter

For fingers

This goniometer is used for the branch of medicine but I wear it so that you know it. Measure the range of motion of the small joints.

fingure goniometer

Other Type of Goniometers

  • Audio goniometers:  In sound production, a signal contains stereo or mono qualities, which are related to the sources of the sound. Sound and recording engineers use audio goniometers to measure the amount of stereo sound present in a given signal.
  • Communications goniometers : Communications goniometers locate the address from where the communication data originates. Because of this, the military and various intelligence agencies primarily use communications goniometers.
  • Crystallography goniometers : Crystallography goniometers measure the angle that appears between the different surfaces of the crystal. This information has several uses for identifying rock and mineral types.
  • Therapeutic goniometers  Physical and occupational therapists use goniometers to measure the range of motion that patients display during therapy sessions. This helps therapists monitor and measure the progress of patients.
  • Scientific Goniometers: Scientific  angle goniometers measure surface tension and are most often used for Earth and physical sciences. Gonio reflections measure how reflective a surface is.
  • Positioning Goniometer:  A positioning goniometer or goniometric stage is used to rotate an object in space at an exact angle around a fixed point on the mounting surface of the device or stage. It uses a worm drive that can be rotated manually or with a motor.

Goniometer reading

The reading is practically the same for all measuring instruments that use a vernier scale, the zero indicates the value of the main scale and a line that coincides with the main scale must be found for the second value. In this case we have to know that the main scale is in degrees and the vernier scale is in minutes.

Image measurement 50 degrees 20 minutes.

Goniometer reading

Why are minutes used?

When it comes to angular measurements we always hear that they say 40 degrees and 25 minutes. Which can lead us to confusion, about what the minutes indicate in that measure.

It is only a matter of technique, a degree is divided into 60 equal parts which we call minutes, instead of saying this angle measures 0.45 degrees, this angle measures 0 degrees 45 minutes.

Do not forget that when divided into 60 parts, 60 minutes equals 1 degree.

Why is the goniometer important in the physical therapy evaluation?

The goniometer is an extremely important instrument in the physiotherapeutic evaluation since it allows to know in what mobility conditions the affected segment or structure arrived (degrees of joint limitation) and the a posteriori advances that the treatment sessions will generate with respect to the primary functional limitation.

It is a precise element that determines the degree of functional limitation of the patient.

Physiotherapy Goniometer

A goniometer is an instrument used to measure angles. Goniometers are used by healthcare professionals to measure the range of motion of a joint in the body.

What is a Physiotherapy Goniometer?

The goniometer comes from the Greek words gonna, which means angle, and metron, which means measure. A goniometer is an instrument used to measure angles. Health professionals use a goniometer to measure the range of motion of a joint in the body. Different types include finger goniometers, bubble goniometers, gravity goniometers, and recording electro-goniometers. They are usually made of plastic, but they can be made of metal in some cases.

A goniometer can measure active and passive range of motion. This can be useful for work tests, workspace design, and other health assessments. It is often used to measure range of motion before a treatment program and again after the program is completed to analyze the improvement that has been achieved.

The traditional physiotherapy goniometer can be used to measure flexion, extension, abduction, adduction, and rotation at the shoulder, elbow, wrist, hip, knee, and ankle. It is made up of a circular body similar to a protractor with a scale from 0 to 180 or 0 to 360 degrees, and two arms. The center of the body is positioned over the joint being measured and the arms are moved until they align with the bones that articulate at that joint.

physiotherapy goniometers

How physiotherapy goniometers work when used

A goniometer consists of two members, usually made of plastic or wood, that are connected by a joint and are generally attached to a circular piece of the same material that is labeled with multiple angular measurements. When one limb is moved to or from the other limb, it drags along the circular piece and displays a measurement. Goniometers are made from a variety of different materials and vary dramatically in size, depending on the nature of the application.


Medical professionals use goniometers to measure the range of motion found in a patient’s appendix before and after treatment to determine if treatment is actually improving the patient’s condition. Goniometers are used in art for an artist to draw a perfectly round straight line or circle. Furthermore, goniometers measure the angle of each face in a crystal structure and have led to a greater understanding of the atomic structure of a crystal.


Goniometers are portable and simple enough to be mass produced in a short period of time. They are inexpensive and serve many different purposes, from those found in the medical industry to applications in the physical sciences. Goniometers have been in use for over two hundred years and have contributed to the advancement of many different fields.


Goniometers must be carefully labeled with respect to the angles they measure. Goniometers are limited by the materials from which they can be constructed and must be used in conjunction with a surface medium to provide meaningful results.

Use of the physiotherapy goniometer

  • Place the goniometer on the fulcrum of the joint. This will vary depending on the joint you are measuring. Place the stationary arm of the goniometer along the stationary line of the body and the movable arm on the movable part of the body.
  • Ask your patient to move the joint in the desired direction. Move the patient to full range of motion, following the motion with the movable arm of the goniometer. Make sure the stationary arm remains straight.
  • Stabilize the stationary portion of the body. This is the part of the body that is proximal (closest to the body’s midline) of the joint you are testing. It is important that the patient does not move his body while moving the joint; this step isolates the movement of the joint for a more accurate measurement.
  • Observe the reading on the goniometer before removing it from the patient’s body. Make sure to take an accurate reading of the degree of movement on the goniometer and to constantly use the same fixed and moving reference points on the body when measuring to ensure consistency. Be sure to record the range of motion of the joint.

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