ISO/IEC 80000

Subject areas

By 2021 the 80000 standard had 13 published parts. A description of each part is available online, with the complete parts for sale.

Part 1: General

ISO 80000-1:2022 revised ISO 80000-1:2009, which replaced ISO 31-0:1992 and ISO 1000:1992. This document gives general information and definitions concerning quantities, systems of quantities, units, quantity and unit symbols, and coherent unit systems, especially the International System of Quantities (ISQ). The descriptive text of this part is available online.

According to the standard, symbols for quantities are "generally single letters from the Latin or Greek alphabet" and are "written in italic (sloping) type". Examples include

• density of heat flow rate: q = Φ / A
• electric current density: J = I / A
• magnetic flux density: B = Φ / A

Part 2: Mathematics

ISO 80000-2:2019 revised ISO 80000-2:2009, which superseded ISO 31-11. It specifies mathematical symbols, explains their meanings, and gives verbal equivalents and applications. The descriptive text of this part is available online.

Part 3: Space and time

ISO 80000-3:2019 revised ISO 80000-3:2006, which supersedes ISO 31-1 and ISO 31-2. It gives names, symbols, definitions and units for quantities of space and time. The descriptive text of this part is available online.

A definition of the decibel, included in the original 2006 publication, was omitted in the 2019 revision, leaving ISO/IEC 80000 without a definition of this unit; a new part of the standard, IEC 80000-15 (Logarithmic and related quantities), is under development.

Part 4: Mechanics

ISO 80000-4:2019 revised ISO 80000-4:2006, which superseded ISO 31-3. It gives names, symbols, definitions and units for quantities of mechanics. The descriptive text of this part is available online.

Part 5: Thermodynamics

ISO 80000-5:2019 revised ISO 80000-5:2007, which superseded ISO 31-4. It gives names, symbols, definitions and units for quantities of thermodynamics. The descriptive text of this part is available online.

Part 6: Electromagnetism

IEC 80000-6:2022 revised IEC 80000-6:2008, which superseded ISO 31-5 as well as IEC 60027-1. It gives names, symbols, and definitions for quantities and units of electromagnetism. The descriptive text of this part is available online.

Part 7: Light and radiation

ISO 80000-7:2019 revised ISO 80000-7:2008, which superseded ISO 31-6. It gives names, symbols, definitions and units for quantities used for light and optical radiation in the wavelength range of approximately 1 nm to 1 mm. The descriptive text of this part is available online.

Part 8: Acoustics

ISO 80000-8:2020 revised ISO 80000-8:2007, which revised ISO 31-7:1992. It gives names, symbols, definitions, and units for quantities of acoustics. The descriptive text of this part is available online.

It has a foreword, scope introduction, scope, normative references (of which there are none), as well as terms, and definitions. It includes definitions of sound pressure, sound power, and sound exposure, and their corresponding levels: sound pressure level, sound power level, and sound exposure level. It includes definitions of the following quantities:

• logarithmic frequency range
• static pressure
• sound pressure
• sound particle displacement
• sound particle velocity
• sound particle acceleration
• volume flow rate, volume velocity
• sound energy density
• sound energy
• sound power
• sound intensity
• sound exposure
• characteristic impedance for longitudinal waves
• acoustic impedance
• sound pressure level
• sound power level
• sound exposure level
• reverberation time

Part 13: Information science and technology

IEC 80000-13:2025 revised IEC 80000-13:2008, which replaced subclauses 3.8 and 3.9 of IEC 60027-2:2005 and IEC 60027-3. It defines quantities and units used in information science and information technology, and specifies names and symbols for these quantities and units. It has a scope; normative references; names, definitions, and symbols; and prefixes for binary multiples.

Quantities defined in this standard are:

• traffic intensity, A: "number of simultaneously busy resources in a particular pool of resources"
• traffic offered intensity, A₀: "traffic intensity ... of the traffic that would have been generated by the users of a pool of resources if their use had not been limited by the size of the pool"
• traffic carried intensity, Y: "traffic intensity ... of the traffic served by a particular pool of resources"
• mean queue length, L (or Ω): time average of queue length
• loss probability, B: "probability for losing a call attempt"
• waiting probability, W: "probability for waiting for a resource"
• call intensity, calling rate, λ: "number of call attempts over a specified time interval divided by the duration of this interval"
• completed call intensity, μ: "call intensity ... for the call attempts that result in the transmission of an answer signal"
• storage capacity, storage size, M
• equivalent binary storage capacity, M_e
• transfer rate, r (or ν)
• period of data elements, T
• binary digit rate, bit rate, r_b, r_bit (ν_b, ν_bit)
• period of binary digits, bit period, T_b, T_bit
• equivalent binary digit rate, equivalent bit rate, r_e (or ν_e)
• modulation rate, line digit rate, r_m, u
• quantizing distortion power, T_Q
• carrier power, P_c, C
• signal energy per binary digit, E_b, E_bit
• error probability, P
• Hamming distance, d_n
• clock frequency, clock rate, f_cl
• decision content, D_a
• information content, I(x)
• entropy, H
• maximum entropy, H₀ (or H_max)
• relative entropy, H_r
• redundancy, R
• relative redundancy, r
• joint information content, I(x, y)
• conditional information content, I(x|y)
• conditional entropy, mean conditional information content, average conditional information content, H(X|Y)
• equivocation, H(X|Y)
• irrelevance, C
• transinformation content, T(x, y)
• mean transinformation content, T
• character mean entropy, H′
• average information rate, H*
• character mean transinformation content, T′
• average transinformation rate, T*
• channel capacity per character; channel capacity, C′
• channel time capacity; channel capacity, C*

The standard also includes definitions for units relating to information technology, such as the erlang (E), bit (bit), octet (o), byte (B), baud (Bd), shannon (Sh), hartley (Hart), and the natural unit of information (nat).

Clause 4 of the standard defines standard binary prefixes used to denote powers of 1024 as 1024¹ (kibi-), 1024² (mebi-), 1024³ (gibi-), 1024⁴ (tebi-), 1024⁵ (pebi-), 1024⁶ (exbi-), 1024⁷ (zebi-), 1024⁸ (yobi-), 1024⁹ (robi-), and 1024¹⁰ (quebi-).

International System of Quantities

Part 1 of ISO 80000 introduces the International System of Quantities and describes its relationship with the International System of Units (SI). Specifically, its introduction states "The system of quantities, including the relations among the quantities used as the basis of the units of the SI, is named the International System of Quantities, denoted 'ISQ', in all languages." It further clarifies that "ISQ is simply a convenient notation to assign to the essentially infinite and continually evolving and expanding system of quantities and equations on which all of modern science and technology rests. ISQ is a shorthand notation for the 'system of quantities on which the SI is based'."

Units of the ISO and IEC 80000 series

The standard includes all SI units but is not limited to only SI units. Units that form part of the standard but not the SI include the units of information storage (bit and byte), units of entropy (shannon, natural unit of information and hartley), and the erlang (a unit of traffic intensity).