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 agents does an e-commerce call center need?

It varies widely based on your order volume and self-service deflection rate. An e-commerce business handling 200 calls per hour with 4-minute AHT at 80/20 service level needs about 15-17 raw agents, or 21-24 after shrinkage. During holiday season, multiply by 1.5-1.7x.

How do I staff for Black Friday and holiday season?

Start planning 10-12 weeks before peak season. E-commerce holiday volume typically increases 50-70% above baseline. Use a combination of seasonal hires (start training by October), extended operating hours, and increased self-service options. Model your peak separately using the seasonal toggle above.

What AHT should I expect for e-commerce support?

The median is about 4 minutes (240 seconds). Order status calls average 2-3 minutes, simple returns 3-4 minutes, and complex issues (payment disputes, missing items) can exceed 6 minutes. If you have strong self-service for order tracking, your phone AHT may be higher since only complex issues reach agents.

Can I run higher occupancy for e-commerce agents?

Yes. E-commerce support calls are generally shorter and more transactional than B2B or healthcare calls, so agents can handle higher occupancy (80-88%) without the same burnout risk. However, if your phone channel primarily handles escalated issues from frustrated customers, keep occupancy closer to 80% to give agents recovery time.

How do flash sales affect staffing?

Flash sales and promotional events can spike call volume 2-3x within 60 minutes of launch. If possible, schedule flash sales during fully-staffed periods. Alert your team in advance, have overflow agents on standby, and ensure your IVR prominently offers self-service options for common questions like promo code issues.

Call Optix

Integrations Pricing Customers

Call Optix

E-Commerce & Retail

E-Commerce Call Center Staffing Calculator

Erlang C calculator with e-commerce and retail benchmarks. Plan staffing for order support, returns processing, and holiday season surges.

Start Calculating

Seasonal Planning:

Standard call volume — no seasonal adjustment applied

Call Center Parameters

Calls Per Hour200

Total incoming calls per hour across all lines

Average Handle Time (AHT)4m

Includes talk time + after-call work

Target Service Level80%

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

Target Answer Time20s

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

17 raw + 7 for shrinkage

Service Level

81.04%

Avg Speed of Answer

16.8s

Occupancy

78.43%

Probability of Wait

25.73%

Immediate Answer

74.27%

Traffic Intensity

13.33 Erlangs

Estimated Staffing Cost

Per Hour

$408

Per Month (160 hrs)

$65,280

E-Commerce & Retail Benchmarks

AHT Range

2m 30s – 6m

Median: 4m

Service Level Standard

80/20

Occupancy Target

80-88%

Acceptable Abandonment

< 5%

Typical Shrinkage

25-30%

Source: ContactBabel US Contact Center Decision-Makers Guide, 2025

Call Center Staffing for E-Commerce & Retail

E-commerce call centers experience some of the most dramatic seasonal swings in any industry. Holiday season can increase call volume by 50-70% above baseline, and flash sale events like Black Friday or Prime Day create intra-day spikes that can overwhelm even well-staffed teams. The cost of inadequate staffing during these peaks is measured in abandoned carts, negative reviews, and lost customer lifetime value.

Unlike B2B operations where each call represents a high-value transaction, e-commerce support handles high volume at relatively lower AHT. Calls tend to be more transactional — order status, return processing, payment issues — which means agents can be trained faster but occupancy rates can safely run higher (80-88%) without significant burnout risk.

The channel mix also matters for staffing. Many e-commerce customers prefer chat or self-service, so your phone channel may handle a smaller percentage of total contacts but tends to get the more complex issues. Customers who call are often frustrated by failed self-service attempts, which means phone agents need strong de-escalation skills and the authority to resolve issues quickly.

Key Challenges

•Holiday season creates 50-70% volume spikes requiring temporary staffing
•Flash sale events (Black Friday, Prime Day) cause unpredictable intra-day surges
•High volume but relatively transactional — AHT is lower than most industries
•Post-purchase support (tracking, returns, exchanges) dominates call mix
•Phone callers are often already frustrated from failed self-service

Common Call Types

Order status and tracking inquiriesReturns and exchange requestsPayment and billing issuesProduct information and availabilityShipping and delivery problemsAccount managementPromotional code and pricing questions

Staffing Tips

1Model holiday season (Nov-Jan) as a completely separate staffing plan — use seasonal hires and extended hours
2Staff for the hour after major marketing emails and flash sale launches; call volume can spike 2-3x within 60 minutes
3Higher occupancy targets (80-88%) are acceptable for transactional e-commerce support vs. complex B2B
4Invest in IVR for order tracking and return status — these high-volume, low-complexity calls can be deflected
5Schedule more agents for Mondays and the day after holidays when customers catch up on orders and issues

Compliance Note

PCI-DSS compliance required for payment processing over phone. Consumer protection regulations (FTC rules on refunds, warranties). GDPR/CCPA compliance for customer data handling.

FAQ

E-Commerce & Retail Staffing FAQ

Turn support calls into repeat customers.

Call Optix analyzes every customer service call — identifying resolution quality, upsell opportunities, and customer sentiment. Reduce churn by catching frustrated customers before they leave a negative review.

You've planned your staffing. Now make sure every customer interaction builds loyalty.

Learn More

Related Industry Calculators

B2B SaaS Sales

40 calls/hr · 7m AHT

Telecommunications

250 calls/hr · 7m AHT

View all industry calculators