Call Center Staffing (Erlang C) & Service Level Calculator
Calculate agent staffing needs to meet service level agreements. Enter values for instant results with step-by-step formulas.
Worked Examples
Example 1: Standard SLA
Problem: 100 calls/hr, 5 min AHT. Target 80/20.
Solution: Traffic = 8.33 Erlangs. Need ~11-12 agents.
Result: 12 Agents
Example 2: High Volume
Problem: 500 calls/hr, 3 min AHT. Target 90/10.
Solution: Traffic = 25 Erlangs. Need ~30 agents.
Result: 30 Agents
Frequently Asked Questions
What is Erlang C?
A mathematical formula derived by A.K. Erlang in 1917 to determine the number of telephone circuits needed. In call centers, it calculates staffing based on queuing theory (assuming calls wait in a queue).
How do I lower staffing needs?
Reduce AHT (better training/tools) or Reduce Volume (Deflection/Self-Serve).
Why might my result differ from another tool or reference?
Differences typically arise from rounding conventions, the specific version of a formula (for example, simple vs compound interest), or unit inconsistencies between inputs. Check that both tools are using the same formula variant and the same units. The References section links to the authoritative source behind the formula used here.
How do I verify Call Center Staffing (Erlang C) & Service Level Calculator's result independently?
The Formula section on this page shows the equation used. You can reproduce the calculation manually or in a spreadsheet using those steps. Compare your answer against the worked examples in the Examples section, which use known reference values so you can confirm the calculator is behaving as expected.
How do I interpret the result?
Results are displayed with a label and unit to help you understand the output. Many calculators include a short explanation or classification below the result (for example, a BMI category or risk level). Refer to the worked examples section on this page for real-world context.
How do I get the most accurate result?
Enter values as precisely as possible using the correct units for each field. Check that you have selected the right unit (e.g. kilograms vs pounds, meters vs feet) before calculating. Rounding inputs early can reduce output precision.