What does erlang mean?
An erlang is a dimensionless unit used in telecommunications to measure traffic intensity — specifically, the amount of demand placed on a set of channels or circuits. One erlang corresponds to one channel being occupied continuously for the duration of an hour, so ten simultaneous hour-long calls would represent ten erlangs. The unit is named after Agner Krarup Erlang, a Danish mathematician who pioneered queueing theory while working for the Copenhagen Telephone Company in the early twentieth century. Engineers rely on erlang-based formulas, notably Erlang B and Erlang C, to determine how many trunks, lines, or agents are needed to handle expected call volumes at acceptable levels of blocking or waiting. Beyond telephony, the concept extends naturally to any congestion-prone system, including call centers and data networks, making the erlang a small but foundational piece of modern communications infrastructure.
nounA dimensionless unit of telecommunications traffic intensity, equal to the continuous use of one voice channel by one call for one hour; used to measure and size telephone network capacity.
- A unit of telecommunications traffic equal to one hour of continuous occupancy of one channel or circuit.
"The switch was provisioned to handle 200 erlangs of peak traffic without blocking calls."
"The support hotline averages 15 erlangs during business hours."
"Using the Erlang C formula, engineers calculated how many agents were needed to handle 40 erlangs of inbound call volume."
Regular plural; typically used with numerals when quantifying aggregate traffic load.
"The trunk group carries roughly 120 erlangs at busy hour."
Every phone network on Earth sizes its trunk lines using a unit invented by a Danish mathematician who worked out queueing math while managing a telephone exchange's coin-collecting boxes.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of erlang
The word derives from the name of Agner Krarup Erlang (1878–1929), a Danish mathematician and engineer credited with founding the mathematical study of telephone traffic and queueing systems. While working at the Copenhagen Telephone Company, he developed models of congestion that made it possible to predict how many circuits a network required. In recognition of this work, the international telecommunications community adopted his surname as the standard unit of traffic intensity. His name also lives on in the Erlang programming language, created at Ericsson and deliberately named after him because it was designed for building highly reliable telephone systems.
How erlang is actually used
Technical register, used almost exclusively in telecommunications engineering and call-center workforce planning. The unit is capitalized when part of eponymous formulas (Erlang B, Erlang C) but usually lowercased as a unit of measure.
Easily confused with erlang
The capitalized Erlang is also the name of a functional programming language developed at Ericsson, named after the same Danish mathematician but entirely distinct from the traffic unit.