Overview of Standard Units of Measurement
Many kinds of units of measurements have been used indigenously in different places over different periods of time and new units have been introduced as and when needed. But the need for universal conformity gave birth to the standard system of measurements, what is known as the S.I. unit today.
What is the S.I. Unit of Measurement?
The S.I. unit is actually an abbreviation of the French word “Système International”. The S.I. unit is the standard system of measurements which are universally accepted and used for technical publishing and scientific research.
International System of Units
Earlier, people didn't have measuring units to calculate the standard measurement units. So, they came up with unique ways of measurement with the tools which were available to them. The foot was used as a measurement for length. 1 foot was calculated as .
To solve the problem of different measurements, a common system of units called the international system of units was found and accepted. This is the modern version of the metric system. Though this system is now being used in all fields including science and technology, some people, especially in the USA, refer to length as foot and inches instead of centimetres.
Apart from the seven base units of measurement, some units are calculated based on one or more base units. These units are known as derived units.
Examples of such units are
Power: watt (W)
Frequency: hertz (Hz)
There are seven base units measurements namely meter, kilogram, second, ampere, kelvin, mole, and candela.
(Image will be uploaded soon)
The most common among these are kilograms, seconds, and meters.
Why are Standard Units Used in Measurement?
Standard units are used in measurement for more accuracy. The measurement should be the same for all. As there needs to be uniformity in the measurement, we must have a common set of units in measurement. These are called standard units.
The standard unit is different for different quantities.
What is a Standard Unit of Measurement?
The standard unit of measurement is a value that is fixed and cannot be changed. It is needed to have uniformity in measurement. The measurement is measured as feet, inches, and pounds in the United States and meters, centimetres, and kilograms in the metric system.
Standard vs Non-Standard Measurements
There are two types of measurements, namely Standard and non-Standard.
Standard measurement units are those which are used within the measurement system such as ounces, inches, and pounds.
The Advantages of Standard Unit are:
It helps everyone to understand measurements in a set of unit systems.
SI units are derived from one another without the use of conversion
SI is a metric system. The disadvantages are that the SI unit talks only about one unit. Hence other units' importance was diluted.
Nonstandard measurement units are those which are not used like a pencil, arm, and block.
The advantage of Nonstandard measurement is it makes measurement easier while the disadvantage is it might be tough for many to understand.
Advantage of SI Units
SI units are measured all over the world.
There is only one unit for each quantity.
Submultiples and multiples can be expressed as multiples of ten as it is a metric system
Measurement of Physical Quantities
A physical quantity is the property of an object that can be measured. Examples of physical quantities are the mass of a body or the length of an object. There are two types of physical quantities namely base quantities and derived quantities.
Base quantities are length, mass, time, luminous intensity, temperature, current, and amount of substance
Derived quantities are those which are derived from other physical quantities. Ex acceleration, velocity, and force.
SI Unit Prefixes
The SI system uses a standard system of prefixes to the basic units which makes it more relevant.
Prefixes are used to identify the fractions Ir multiples of the basic unit. There are 20 acceptable prefixes.
SI Base Units
These units of measurement are considered to be the fundamental units and all the other units can be derived from the SI base units.
Unit of Mass (kilogram): Kilogram is defined by taking the fixed value of Planck’s constant in kilogram per meter square per second. It is abbreviated as kg.
Unit of Length (Meter): Abbreviated as “m”, meter is defined by taking the value of speed of light in vacuum in meter per second.
Unit of Time (Second): A second is defined as the value obtained by taking the value of each Cesium frequency. Its abbreviation is “s”.
Unit of Electric Current (Ampere): Abbreviated as “A”, it is obtained by taking the fixed value of elementary charge.
Unit of Temperature (Kelvin): Although Fahrenheit and Celsius are the more commonly used measurements of temperature, the SI unit of temperature is Kelvin, abbreviated as K. Its value is equal to the Boltzmann constant. 10C = 273 K.
Unit of an Amount of Substance (Mole) : One mole contains 6.02214076×1023 elementary entities which is the constant of Avogadro’s number and is expressed as mol-1.
Unit of Luminous Intensity (Candela) : Defined by the fixed value of luminous efficacy, the SI unit of luminous intensity is candela and is expressed as “cd”.
Note: The 7 base units are considered to be mutually independent from which the other units of measurement can be derived.
The derived SI units are unlimited and are in a continuous process of development resulting from scientific research and can be based either solely on the base units or they can be a combination of base units and other already established derived units.
There are a few additional SI units that are very commonly used in Physics, such as, “joule” which is the SI unit of heat and “Tesla” which is the SI unit of magnetic field.
Students are suggested to have a thorough understanding of these units in Physics and their dimensions. Vedantu's notes, important questions and revision topics will help you clear your basics on SI unit of measurement. You can even download the references for free! Go ahead with a curious mind and come back as a champ!
FAQs on Standard Units of Measurement
1. What is a standard unit of measurement?
A standard unit of measurement is a universally accepted, fixed quantity used as a reference to measure other physical quantities of the same kind. For example, the metre is the standard unit for length. Using standard units ensures consistency and uniformity in measurements across different locations and contexts, preventing confusion and errors.
2. What are the seven fundamental SI units and the quantities they measure?
The International System of Units (SI) is built upon seven fundamental (or base) units. All other physical units can be derived from these. As per the CBSE 2025-26 syllabus, the seven fundamental units are:
- Metre (m) for length
- Kilogram (kg) for mass
- Second (s) for time
- Ampere (A) for electric current
- Kelvin (K) for thermodynamic temperature
- Mole (mol) for the amount of substance
- Candela (cd) for luminous intensity
3. What are derived units? Provide some common examples found in Physics.
Derived units are units of measurement that are formed by combining the seven fundamental SI units through multiplication or division. They are used to measure physical quantities other than the base quantities. Some common examples include:
- The unit of velocity (metre per second, m/s), derived from length and time.
- The unit of force (newton, N), which is equivalent to kg⋅m/s².
- The unit of energy (joule, J), which is equivalent to a newton-metre (N·m).
4. What are the main systems of units used in measurement besides the SI system?
While the SI system is the most widely used standard globally, other systems are also important to understand. The main ones are:
- CGS System: Based on the centimetre, gram, and second as fundamental units for length, mass, and time.
- MKS System: Based on the metre, kilogram, and second, which formed the basis for the modern SI system.
- FPS System: Based on the foot, pound, and second, also known as the British or Imperial system, still used in some contexts.
5. Why is it necessary to have a standard system of units like the SI system?
A standard system of units is crucial for several reasons. It establishes uniformity, allowing scientists, engineers, and traders worldwide to communicate and collaborate without ambiguity. It simplifies calculations as it is a decimal-based (metric) system, making conversions between multiples and sub-multiples straightforward (e.g., 1 kilometre = 1000 metres). This global standardisation is essential for scientific research, international trade, and technological development, ensuring that a measurement of 'one kilogram' is the same everywhere.
6. How do standard units of measurement differ from non-standard units?
The primary difference lies in their consistency and universality.
- Standard units, like the metre or kilogram, are fixed, well-defined, and universally accepted. Their value does not change, ensuring that measurements are reproducible and understood by everyone.
- Non-standard units, such as a handspan or a footstep, are inconsistent and subjective. Their value varies from person to person, making them unreliable for precise or scientific communication. For instance, one person's 'handspan' will be different from another's.
7. How has the definition of the base SI units, like the kilogram, changed in recent years?
As of the 2019 redefinition, the SI base units are no longer defined by physical artifacts but by fundamental physical constants. For example, the kilogram was previously defined by a physical cylinder of platinum-iridium. Now, its definition is based on a fixed numerical value of the Planck constant (h). Similarly, the metre is defined based on the speed of light in a vacuum (c). This shift ensures the units are more stable, precise, and can be realised anywhere, not just by comparing to a single physical object.
8. How are prefixes like 'kilo-' and 'milli-' used with standard units to represent very large or small quantities?
Prefixes are used in the SI system to create multiples or sub-multiples of the base units, making it easier to express very large or small values. Each prefix represents a power of 10. For example:
- The prefix 'kilo-' (k) means 1000 or 10³. So, 1 kilometre (km) is 1000 metres.
- The prefix 'milli-' (m) means 0.001 or 10⁻³. So, 1 milligram (mg) is 0.001 grams.
- The prefix 'giga-' (G) means 10⁹ (one billion), and 'nano-' (n) means 10⁻⁹ (one-billionth).
