is a brief introduction to the calculator. For more detailed information, press the Help
Button. For a running record of the results calculated, press the Results button.
Both these functions open new browser windows on your desktop.
- The Erlang B traffic model is used by telephone system designers to estimate the number
of lines required for PSTN connections (CO trunks) or private wire connections. The
three variables involved are Busy Hour Traffic (BHT), Blocking and Lines:
- Busy Hour Traffic (in Erlangs) is the number of hours of call traffic there are
during the busiest hour of operation of a telephone system.
- Blocking is the failure of calls due to an insufficient number of lines being
available. E.g. 0.03 mean 3 calls blocked per 100 calls attempted.
- Lines is the number of lines in a trunk group.
- If you know two of the figures, you can work out the third as follows:
- Click on the Unknown radio button representing the unknown variable.
- Enter the 2 known figures into their edit boxes.
- Press Calc and the third figure will be calculated and displayed in the remaining
- For example, if from your call logger, you know that the Busy Hour Traffic is 10
Erlangs, and you want to know how many lines are required in this trunk group if you are
prepared to tolerate 2 calls being blocked in every 100 calls attempted then:
- Press the Lines Unknown radio button (this is selected by default).
- Enter 10 in the BHT edit box.
- Enter 0.02 in the Blocking edit box.
- When you press the Calc button, 17 will be displayed in the Lines edit box
indicating that 17 lines would be required in this trunk group.
The Erlang B Traffic Calculator on this page is modelled
on the Erlang B Calculator included with the Westbay Traffic Calculators for Windows. The
calculator works up to 90,000 Erlangs / Lines and has the ability to display and
print the results of any calculations you have made during the previous week.
Customers also benefit from an Extended Erlang B Calculator, an Erlang C
Calculator for analysing call centres and a Call Minutes Calculator. These calculators are
available for 99 US Dollars. If you pay using VISA,
MasterCard, American Express or Discovery, you can have this software working on
your PC in five minutes!