Free technical white paper · with live Excel workbook
From Erlang to Excel
Contact-centre queueing theory from beginner to expert — and how to rebuild every formula in a spreadsheet you control.
Most planners trust an Erlang calculator without ever seeing inside it. This paper opens the black box. It builds the maths up in order — offered load, Erlang B, Erlang C, then Erlang A with abandonment — explains the assumptions behind each, and then rebuilds the lot, cell by cell, in Excel. It ends where the formulae stop being trustworthy and simulation takes over. Written for the planner who wants to understand the numbers, not just read them.
It opens with a short history of A. K. Erlang himself — the Danish engineer who founded queueing theory to stop Copenhagen’s switchboards jamming — and why his century-old maths still sizes contact centres today.
Read it, or take it with you
Free, no sign-up. The PDF, the live Excel workbook (Erlang B/C/A built in with real formulas), or the full paper online.
Download the white paper (PDF) Download the live Excel workbook Read the full paper onlineWhat’s inside
- The man behind the formulae — who Erlang was, and why his maths still matters
- Offered load in Erlangs, and the assumptions the classical models depend on
- Erlang B — blocking, and the numerically stable recursion that tames it
- Erlang C — probability of waiting, service level, ASA, occupancy, and finding the staffing number
- Erlang A — caller patience and abandonment, from a birth–death state model
- Erlang X — abandonment, blocking and redials together, solved by fixed-point iteration
- Where the formulae break: non-Poisson arrivals, lognormal handle times, the interval boundary, and multi-skill
- When to reach for simulation instead — and which model to use when
- Every formula rebuilt in Excel, cell by cell, with a validation checklist
Includes a live companion workbook. The Excel model has Erlang B, C, A and X built as real, recalculating formulas — the Erlang X sheet solves the redial loop with explicit iteration passes, so it works in any spreadsheet with no settings to enable. Change the inputs and watch service level, ASA, occupancy, abandonment, blocking and redials move. It pairs with the free Erlang C, Erlang A and Erlang X calculators, which use exactly the recursions in the paper.
Part of the ccplanning.net white-paper series.