# Erlang B calculator

This is the original free online Erlang B calculator. Use it to estimate how many lines you need in your trunk groups if you know the traffic that will be offered to your system.

 Erlang B Calculator Erlangs Blocking Lines

## Excel version

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## Erlang B Calculator instructions

Our original Erlang B calculator estimates the number of voice lines you need. The three variables involved are:

• Busy Hour Traffic (in Erlangs): the hours of call traffic during the busiest hour of a telephone system’s operation
• Blocking: the ratio of calls that fail through insufficient lines (e.g. 0.03 means 3 calls blocked per 100 calls attempted)
• Lines: the number of circuits in a trunk group

If you know two of the figures, you can work out the third:

• Click on the button representing the variable you want to calculate (Lines is selected by default)
• Enter the two known figures into their edit boxes
• Press Calculate and the unknown value will be calculated and displayed in the remaining box

For example, if you know that the Busy Hour Traffic is 10 Erlangs and you want to know how many lines you need if you can tolerate 2% of calls being blocked, select the Lines button, enter 10 in the BHT box and 0.02 in the Blocking box. When you press Calculate, the answer (17 lines) will be displayed.

## Excel version

Enjoy the ultimate flexibility of having Erlang functions in your own workbooks. Erlang for Excel adds eight functions to Excel, covering Erlang B, Erlang C and Extended Erlang B.

On the left are three of the many calculators included with Erlang for Excel. You can use them straight away or design your own traffic workbooks with the eight built-in functions – there’s a simple example on the right. With some knowledge of Excel, you can use its more advanced features such as lookup tables, conditional formatting and charting to build complex modelling tools.

We’ve used the Erlang for Excel add-in for years and it works great.
Mark Rolag, xtDirect LLC

We provide free upgrades for life on a single computer for a once-only charge of just \$66. (33% discount)

## Windows version

Westbay Traffic Calculators is a Windows package of four calculators including this Erlang B Calculator. We offer free upgrades and installation support for the lifetime of the product. The calculator works up to 90,000 Erlangs / Lines and can display and print the results of the previous week.

Our best-selling Windows application comprises four calculators for Erlang B and Erlang C. Use them to dimension trunk groups and predict the performance of your help desk or call center agents.

“Beats the heck out of lugging around your Erlang tables. I recommend this product highly.”
Computer Telephony Magazine

Free upgrades for life on a single computer for a once-only charge of just \$99.