What is the Erlang C formula and how does it work?

Erlang C is a mathematical formula that calculates the probability of a caller having to wait in a queue, given the number of agents, call volume, and average handle time. It models the random arrival pattern of calls using Poisson distribution, making it far more accurate than simple division-based staffing estimates. The formula was developed by Danish mathematician A.K. Erlang and is the global standard for call center workforce planning.

What is the difference between Erlang B and Erlang C?

Erlang B calculates the probability of a call being blocked (receiving a busy signal) in a system with no queue — if all agents are busy, the call is lost. Erlang C, on the other hand, assumes calls will wait in a queue if no agent is immediately available. For most modern call centers with hold queues, Erlang C is the correct formula to use.

What is a good service level target for a call center?

The industry standard is 80/20 — meaning 80% of calls answered within 20 seconds. However, optimal targets vary by industry. Premium support lines may target 90/10, while cost-sensitive operations might accept 70/30. The right target balances customer experience against staffing costs.

What is shrinkage in call center staffing?

Shrinkage is the percentage of time agents are unavailable to handle calls despite being on shift. It includes breaks, lunch, training, meetings, coaching sessions, system downtime, sick leave, and other off-phone activities. Typical shrinkage ranges from 25% to 35%. Accounting for shrinkage is critical — without it, you'll be significantly understaffed.

How do I calculate my Average Handle Time (AHT)?

AHT = Average Talk Time + Average Hold Time + Average After-Call Work (ACW) time. Talk time is the actual conversation duration. Hold time is when the caller is on hold. ACW (or wrap-up time) includes note-taking, CRM updates, and any post-call tasks. Most ACD (Automatic Call Distribution) systems track these components automatically.

What is agent occupancy and what's the ideal rate?

Occupancy is the percentage of time agents spend handling calls versus waiting for calls. An occupancy rate of 80-85% is generally considered ideal. Below 70% suggests overstaffing. Above 90% leads to agent burnout, increased attrition, and degraded service quality as agents have no recovery time between calls.

Is the Erlang C formula accurate?

Erlang C is highly accurate for inbound call center planning and is the industry standard used worldwide. However, it has limitations: it assumes infinite queue capacity (no callers hang up), it doesn't account for call abandonment, and it assumes a steady-state system. For most practical purposes, these limitations are minor, and Erlang C provides excellent staffing estimates.

How often should I recalculate staffing levels?

Recalculate whenever your call patterns change significantly. Most centers review staffing quarterly and adjust for seasonal patterns. You should also recalculate when AHT changes (due to new products, policy changes, or training), when call volume trends shift, or when you change your service level targets.

What is traffic intensity in Erlangs?

Traffic intensity measures the total call workload on your system, expressed in Erlangs. It's calculated as (calls per hour × average handle time in seconds) / 3600. One Erlang represents one agent fully occupied for one hour. You always need more agents than Erlangs — for example, 10 Erlangs of traffic might require 14-15 agents to maintain an 80/20 service level.

Can I use this calculator for chat and email staffing?

Erlang C was designed for single-channel voice calls where agents handle one interaction at a time. For chat (where agents handle multiple simultaneous conversations) or email (which isn't real-time), you'll need modified approaches. However, if your chat agents handle one chat at a time, Erlang C can provide a reasonable estimate.

How many BDC agents does a dealership need?

A typical single-point dealership handling 55 calls per hour with 3.5-minute blended AHT at 80/15 service level needs 6-7 raw agents, or 8-10 after shrinkage. Multi-rooftop dealer groups should model each location separately, then evaluate centralized BDC efficiency.

What AHT should I use for a dealership BDC?

The blended median is about 3.5 minutes (210 seconds). Sales inquiry calls average 4-5 minutes, service scheduling 2-3 minutes, and internet lead follow-up calls 5-7 minutes. Weight your AHT based on your actual call mix between sales, service, and internet leads.

Should sales and service BDC agents be separate?

Ideally yes, especially for staffing calculations. Sales calls peak at different times than service calls, and the skill sets differ. If you blend them, your Erlang C calculation will be less accurate because AHT variance is too high. Model them separately, even if some agents handle both.

How important is internet lead response time?

Extremely. Industry data shows dealerships responding to internet leads within 10 minutes are 3x more likely to set an appointment. Within 5 minutes is even better. Your BDC staffing must ensure that inbound calls from internet leads get immediate pickup — these callers are actively shopping and will move to the next dealer.

How do I staff for year-end clearance events?

Year-end clearance (November-December) typically increases call volume by 30-40%. Start preparing 6 weeks ahead. Options include hiring seasonal BDC agents, extending hours, cross-training sales floor staff for phone coverage, and using AI agents for simple inventory checks and appointment scheduling.

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Automotive Dealership

Automotive BDC Staffing Calculator

Erlang C calculator with automotive dealership benchmarks. Plan staffing for your Business Development Center — sales calls, service appointments, and internet lead follow-up.

Start Calculating

Seasonal Planning:

Standard call volume — no seasonal adjustment applied

Call Center Parameters

Calls Per Hour55

Total incoming calls per hour across all lines

Average Handle Time (AHT)3m 30s

Includes talk time + after-call work

Target Service Level80%

% of calls answered within target time. Industry standard: 80%

Target Answer Time15s

Maximum wait time in seconds. Standard: 20s

ShrinkageShrinkage accounts for breaks, training, meetings, sick time, and other non-productive time that reduces agent availability.28%

Typical range: 25-35%

Cost Per Agent Per Hour (optional)

Fully loaded cost for monthly cost estimate

Agents Needed

6 raw + 3 for shrinkage

Service Level

89.48%

Avg Speed of Answer

9.7s

Occupancy

53.47%

Probability of Wait

12.84%

Immediate Answer

87.16%

Traffic Intensity

3.21 Erlangs

Estimated Staffing Cost

Per Hour

$171

Per Month (160 hrs)

$27,360

Automotive Dealership Benchmarks

AHT Range

2m – 7m

Median: 3m 30s

Service Level Standard

80/15

Occupancy Target

65-78%

Acceptable Abandonment

< 5%

Typical Shrinkage

25-32%

Source: NADA Dealership Workforce Study, 2025

Call Center Staffing for Automotive Dealership

Automotive BDCs (Business Development Centers) serve as the central hub for all inbound customer communication at a dealership. They handle a mix of sales inquiries, service appointment scheduling, internet lead response, and customer follow-up — often with the same team. This blended workload creates unique staffing challenges because AHT varies dramatically by call type.

Speed-to-answer matters enormously in automotive. When a shopper calls about a vehicle they found online, they're likely also looking at competing dealerships. Industry data shows that dealerships responding to internet leads within 10 minutes are 3x more likely to set an appointment than those responding within an hour. Your BDC staffing must ensure near-instant pickup during peak hours.

Automotive call patterns follow both daily and seasonal rhythms. Lunch hours (11am-1pm) and early evenings (5pm-7pm) see the highest sales call volume. Seasonally, year-end clearance events and tax refund season drive significant spikes. Service department calls follow a different pattern, peaking on Monday mornings when customers report weekend issues. Staffing models should account for these distinct patterns.

Key Challenges

•Blended sales and service calls with very different AHTs and skill requirements
•Internet lead response time directly impacts appointment set rates
•Daily call clustering around lunch hours and early evenings
•Year-end clearance and tax season create predictable but intense spikes
•Multi-location dealer groups need centralized vs. distributed staffing decisions

Common Call Types

New vehicle sales inquiriesUsed vehicle availability checksInternet lead follow-upService appointment schedulingParts ordering and inquiriesFinance and lease questionsTrade-in value requests

Staffing Tips

1Separate sales and service queues in your staffing model — they have different AHTs and peak times
2Staff heaviest during 11am-1pm and 5pm-7pm when sales call volume peaks
3Target 15-second answer time for sales calls — shoppers comparing dealers won't wait
4Plan for Monday morning service spikes; schedule more service BDC agents on Mondays
5During year-end clearance events, temporarily reallocate service agents to sales overflow with basic training

Compliance Note

TCPA compliance critical for outbound follow-up calls. FTC Safeguards Rule requires data security for customer financial information. State-specific auto dealer regulations may govern phone sales practices and disclosures.

FAQ

Automotive Dealership Staffing FAQ

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