Free Tool

WFM Staffing Calculator for Contact Centers

An Erlang A calculator that handles voice, chat, and email in one spreadsheet. Built by the team that runs a 600+ seat BPO.

Download the Free Calculator .xlsx file. Works in Excel and Google Sheets. No macros. No signup.

Why we built this

Most free Erlang calculators on the internet do one thing: voice staffing with Erlang C. That's a start. But if you're running a modern contact center, you're handling chat and email too. And Erlang C assumes nobody ever hangs up, which overstaffs you.

We built this calculator at Expivia because we needed something better for our own 600+ seat BPO. It uses Erlang A (which accounts for customer abandonment), handles voice, chat with concurrency, and email with SLA targets. It includes a weekly planner with half-hour intervals and an executive dashboard that auto-generates from your forecast.

We're giving it away because every contact center deserves real math behind their staffing decisions. Not guesswork. Not gut feeling.

What's in the calculator

Tab 1: Calculator

Voice, Chat, and Email Inputs

Enter your call volume, AHT, service level, patience, shrinkage, max occupancy, and cost per hour. Same for chat (with concurrency settings) and email (with SLA targets). Get staffing requirements instantly.

Tab 2: Weekly Plan

Half-Hour Interval Forecast

Enter your call forecast by half hour and day of week. Staffing, peak headcount, and costs auto-calculate. See exactly how many agents you need in every interval.

Tab 3: Dashboard

Executive Summary

Weekly calls, daily average, peak day, agent hours, FTEs needed, peak headcount, weekly cost, annual cost, and cost per call. All auto-generated from your plan.

Tab 4: Engine

The Erlang A Math

Erlang B, Erlang C, and Erlang A probability tables. This powers everything. You don't need to touch it. Just know the math is real.

How to use it

1
Open the Calculator tab. Enter your voice inputs: calls per half hour, average handle time in seconds, service level target (e.g. 0.80 for 80%), answer time in seconds, average patience in seconds, shrinkage rate, max occupancy, and cost per agent hour.
2
Enter chat inputs. Chats per half hour, max concurrent chats (1-3), AHT at each concurrency level, service level target, response time, and shrinkage.
3
Enter email inputs. Emails per hour, average handle time in minutes, response SLA in hours, hours of operation, shrinkage, and cost per agent hour.
4
Read your results. Agents needed on phones (net), scheduled headcount (with shrinkage), occupancy, cost per interval, and annual labor cost. Same breakdowns for chat and email.
5
Go to Weekly Plan. Edit the yellow forecast cells with your actual call volumes by half hour and day of week. Staffing and costs calculate below automatically.
6
Check the Dashboard. Your executive summary is auto-generated. Weekly calls, agent hours, FTEs, peak headcount, costs, cost per call. Share it with your boss.

Erlang A vs Erlang C: Why it matters

Most free calculators use Erlang C. Erlang C assumes every caller waits forever. Nobody hangs up. In reality, customers abandon. They hang up after 60, 90, 120 seconds. Erlang C ignores this and tells you to hire more agents than you actually need.

Erlang A (developed by Conny Palm in 1946) factors in average patience. It models abandonment. The result is a more accurate staffing number that doesn't overstaff you during peaks or waste budget on agents who would be sitting idle.

This calculator uses Erlang A for voice staffing. It also adds occupancy protection (so you don't burn out your team above 85%) and forecast uncertainty adjustment. These are the same factors enterprise WFM platforms account for. Now you have them in a spreadsheet.

How this compares to other free calculators

FeatureMost Free CalculatorsThis Calculator
Erlang modelErlang C onlyErlang A (with abandonment)
Voice staffingYesYes
Chat staffingNoYes (with concurrency)
Email staffingNoYes (SLA-based)
Max occupancy capRareYes
Forecast uncertaintyNoYes
Weekly interval planNoYes (half-hour)
Cost modelingNoYes (per interval + annual)
Executive dashboardNoAuto-generated
Requires signupOftenNo
Requires macrosOftenNo

Who this is for

This calculator is for ops managers, workforce planners, and contact center leaders at centers of any size who need real math behind their staffing. If you're currently estimating headcount from averages or gut feeling, this will change how you plan. If you're paying for enterprise WFM software but only using it for basic staffing, this does the same core math for free.

Download the calculator. It's free.

Built by the team at Expivia. Given away by OttoQA. Because better contact centers start with better math.

Download the Calculator

Frequently asked questions

Does this work in Google Sheets?
Yes. Upload the .xlsx file to Google Sheets and it works. No macros required.
What is Erlang A?
Erlang A is a staffing formula that accounts for customer abandonment (people who hang up before being answered). It was developed by Conny Palm in 1946 as an improvement to Erlang C, which assumes no one ever hangs up. Erlang A gives you more accurate staffing numbers because it reflects what actually happens in your center.
What does "average patience" mean?
Average patience (also called average time to abandon) is the average number of seconds a caller will wait before hanging up. This varies by industry. Healthcare callers tend to wait longer. Sales callers hang up faster. Check your ACD reports for your actual abandonment data.
Why does max occupancy matter?
Occupancy is the percentage of time an agent spends on calls vs waiting. If you push occupancy above 85% for extended periods, agents burn out, AHT increases, quality drops, and attrition spikes. The calculator caps occupancy so your staffing plan is sustainable.
How does the chat calculator handle concurrency?
You set the maximum number of simultaneous chats per agent (1, 2, or 3) and the AHT at each level. AHT increases as agents handle more chats at once. The calculator uses these inputs to determine how many chat agents you need.
Do I need to give my email to download this?
No. Click the download button. The file downloads. That's it.
Who built this?
The workforce management team at Expivia, a 600+ seat USA-based BPO in Erie, PA. OttoQA is our AI-powered QA platform. We built both because we needed them to run our own operation.

More free tools

This calculator is part of our free tools library for contact center leaders. We also offer a QA Form Analyzer that uses AI to evaluate your QA scorecard. More tools are coming. Check the full tools page to see what's available.