About Erlang Calculator
Free, accurate Erlang B and C traffic engineering tools — built for telecom engineers and call center professionals.
Why We Built This
Erlang Calculator exists because telecom traffic engineering math shouldn't require expensive software licenses or a university textbook. Agner Krarup Erlang published his foundational formulas in 1917. The ITU-T has maintained them in the E.500 series recommendations ever since. They're public domain, mathematically precise, and universally applicable — yet the tools to run them have historically been locked inside proprietary workforce management platforms costing thousands of dollars per seat.
We built this calculator for the telecom engineer sizing SIP trunks for a new office, the call center manager who needs to justify a headcount request to finance, the VoIP architect validating that a hosted telephony platform can handle peak concurrency, and the student learning queuing theory for the first time. All of them need the same math. None of them should have to pay for it.
The calculator implements the iterative Erlang B formula for numerical stability (avoiding the factorial overflow that affects direct formula implementations at high traffic loads) and the standard Erlang C formula with service level computation per ITU-T E.501. Our results match those produced by professional WFM platforms including NICE, Genesys, and Verint — the same math, freely accessible here without account creation or subscription.
Telecom-Specific Tools
Every calculation is grounded in real telecom traffic engineering formulas. We implement Erlang B and Erlang C per ITU-T E.501 and cite all sources on every page.
Free, No Strings Attached
No paywalls, no mandatory sign-ups, no hidden fees. The Erlang formulas are public domain and so is our implementation of them.
Verified Accuracy
We cross-validate our results against ITU-T standards and published traffic engineering tables. If you find a discrepancy, we want to know.
Educational Content
Our blog covers traffic engineering, call center staffing, SIP trunk sizing, and more — written for practitioners, not textbook authors.
How We Verify Our Calculations
Our Erlang B implementation uses the numerically stable iterative recurrence B(N,A) = (A·B(N-1,A)) / (N + A·B(N-1,A)) starting from B(0,A) = 1. This avoids the factorial overflow that occurs in the direct formula when traffic intensity exceeds approximately 170 Erlangs. We validate our outputs against published Erlang B tables from Iversen, V.B. — Teletraffic Engineering and Network Planning (Technical University of Denmark, 2015) and the ITU-T E.501 traffic engineering tables.
Our Erlang C implementation calculates the wait probability C(N,A) using the Erlang B intermediate result, then computes service level as SL = 1 - C(N,A) × e^(-(N-A)(t/Ts)) per the standard queuing model. We verify results against the staffing tables in the COPC Inc. Contact Center Operations Management Standard.
Content published on this site is written by telecom practitioners and reviewed for technical accuracy before publication. We update articles and formulas when standards change. Last reviewed: .
Get in Touch
Found a calculation error, have a question about a specific Erlang scenario, or want to suggest a topic for the blog?
contact@example.com