Units of measurement in electronics: what is the The International System of Units?

Units of measurement are the alphabet of the language science uses — and electronics speaks it with exceptional precision. Without understanding fundamental concepts (such as amperes, reactive power, apparent power, active power, henry, ohm, volt, siemens, or coulomb), it is difficult to design, repair, improve, test, or even use electronic components consciously. Are you interested in electronics but unfamiliar with the fundamentals of physics? You’ve come to the right place! We have prepared a practical guide to the basic physical quantities, electrical current measurement units, and their significance in electronics. Enjoy the reading!

Physical quantities and electrical current measurement units: the foundations of physics as the basis for electronics

Physics is built upon specific laws, principles, concepts, and physical quantities that are interconnected, forming a coherent system for describing reality. Describing the laws governing electricity and electronics is impossible without first defining their corresponding physical quantities and measurement units.

What are physical quantities?

A physical quantity is a characteristic of a physical phenomenon or a measurable property of a physical object. It enables mathematical modeling of phenomena and determining parameter values that cannot always be directly measured.

A set of related quantities and their corresponding units forms a system of physical quantities, where we distinguish:

• Fundamental quantities (independent).
• Derived quantities (defined based on fundamental ones).

An example of a fundamental quantity is electric current.

Physical quantities in electronics

Which physical quantities do we use in electronics and electrical engineering? Here are the most important ones:

• Electrical voltage (U) – the difference in electrical potential between two points. It determines the flow of electric current.
• Electric current intensity (I) – the amount of electrical charge flowing through a conductor within a specific unit of time.
• Electrical resistance (R) – the opposition a material presents to electric current. This principle allows dimmer switches to regulate light brightness. If resistance occurs between two contaminated surfaces, the flow of electric current will be restricted — when cleaning dirty electronic components, using a specialized cleaning agent like Kontakt IPA Plus is recommended.
• Speed – the rate of change of an object’s position over time; it is essential in electronics, particularly for signal transmission.

Other important physical quantities:

• Temperature – a crucial parameter in designing systems prone to overheating. In industrial and maintenance applications, thermal conductive pastes and thermal adhesives (ThermoConductivity) are useful.
• Mass and weight – fundamental mechanical parameters of physical objects.
• Force – the effect of mechanical, electrical, or magnetic interactions.

This practical foundation provides a crucial understanding of the role these quantities play in electronics — making designing, troubleshooting, and optimizing electronic systems much more effective!

What are units of measurement?

Physical quantities can be measured, meaning numerical values can be assigned to them. These values must be expressed relative to an accepted unit of measurement — a defined value of a given physical quantity that serves as the reference standard. A unit of measurement is therefore a fixed numerical value equal to 1 (one).

A set of accepted units forms a system of units. In Poland, we use The International System of Units (SI) (from the French Système International d’Unités).

Systems of units – a historical overview

The The International System of Units is an unified, international system of measurement that has enabled scientists worldwide to communicate freely and compare research results. It forms the foundation of modern science and engineering.

SI is the first universally adopted system, though it has not been officially accepted in three countries: Myanmar, Liberia and The United States. Historically, however, SI was not the first system created — previously, various measurement systems were used, including:

• CGS (centimetre-gram-second) – defined in 1874, particularly popular among theoretical physicists. It played a crucial role in standardizing measurement units. While the CGS system is now largely obsolete, some of its derived units (such as gauss and barye) are still used in certain fields.
• MKS (metre-kilogram-second) – adopted in 1889, widely used in engineering and classical physics. It became an internationally recognized system in the early 20th century.
• MKSA (metre-kilogram-second-ampere) – the predecessor of the SI system.
• MTS (metre-tonne-second) – the least commonly used variant.

Before the establishment of international systems, each country independently defined its measurement units.

The International System of Units – origin and significance

The International System of Units (SI) was officially approved in 1960 and has been used in Poland since 1966. However, efforts to standardize the system began as early as 1948.

A major update to the SI system was introduced in 2019, when several fundamental units were redefined based on physical constants (such as Planck’s constant and elementary charge). As a result, the definitions of kilogram, ampere, kelvin and mole are no longer dependent on physical objects or experimental setups, but are instead based on universal physical constants.

The International System of Units – characteristics

In The International System of Units (SI), we distinguish two main groups of units that form a cohesive, hierarchical system:

• Fundamental units – defined independently, either through experiments or fundamental physical constants. An example is the metre, which is determined as the distance traveled by light in a vacuum in 1/299,792,458 seconds.
• Derived units – based on fundamental units, created through mathematical equations and relationships. An example is the newton (N) — the unit of force — calculated as the product of kilograms and meters per second squared (1 N = 1 kg × 1 m/s²). Since kg, m, and s are all fundamental units, they serve as the foundation for derived measurements.

If you want to explore the full list of fundamental and derived SI units, their historical origins, notation methods, or fascinating facts about metrology, you should refer to the official document from the International Bureau of Weights and Measures (BIPM). Based on this, the article “Compendium of Main Rules and Practices Applicable to the BIPM” has been made available for review by the Central Office of Measures, Poland’s official metrology institution.

SI base units – definitions of fundamental units

The International System of Units (SI) focuses on seven fundamental measurements. All other units can be derived from these. The seven SI base units are:

1. Metre (m) – unit of length (l) – essential for designing PCB layouts.
2. Kilogram (kg) – unit of mass (m) – used as a fundamental value in force calculations for mechanical components.
3. Second (s) – unit of time (t) – crucial for synchronizing digital circuits and signals.
4. Ampere (A) – the primary unit of electric current (I) – describes the amount of charge flowing per unit of time.
5. Kelvin (K) – unit of temperature, primarily used in scientific applications to measure absolute (thermodynamic) temperature.
6. Candela (cd) – unit of luminous intensity – applied in lighting technology and calibration of optical sensors.
7. Mole (mol) – unit of amount of substance (n) – important in chemical analysis, including for manufacturing electronic components and insulating materials.

The second major category of SI units consists of derived units, which are created by combining base units using algebraic formulas. Stay tuned — we’ll dive into these soon! We’ll continue our physics fundamentals series, so be sure to follow our blog, where we share specialized knowledge.

Summary

Every electronics engineer and electrician should be familiar with SI measurement units and know how to use them effectively. Whether you’re just beginning your electronics journey or already have extensive experience, remember that electronics isn’t just about working with inntegrated circuits — it’s also about the mathematical equations that form its foundation.