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.

Can I use Erlang C for a sales team?

Yes, with caveats. Erlang C was designed for inbound call queues where callers wait for the next available agent. It works well for modeling inbound sales teams that receive demo requests and qualification calls. It's less applicable for outbound-only teams, but most SaaS sales teams have a significant inbound component that benefits from Erlang C modeling.

What AHT should I use for SaaS sales calls?

The median AHT for blended inbound SaaS sales is around 7 minutes (420 seconds). Quick qualification calls may be 3-5 minutes, while full discovery calls run 15-20 minutes and demos can exceed 30 minutes. For Erlang C, use a weighted average based on your call mix. If 60% are short qualifications and 40% are longer demos, weight accordingly.

Why is SaaS sales shrinkage so high?

SaaS sales reps have more non-call activities than traditional call center agents: pipeline reviews, CRM data entry, deal strategy meetings, product training on new features, competitive intelligence briefings, and one-on-one coaching. Additionally, many reps do both inbound and outbound, and outbound prospecting time is effectively shrinkage from an inbound-queue perspective.

What occupancy rate should a sales team target?

Lower than a support center: 60-75% is typical for sales teams. Sales calls require preparation (reviewing the prospect's company, recent activity, CRM notes) and post-call follow-up (sending decks, writing proposals). Running reps at 85%+ occupancy leads to unprepared calls, poor follow-up, and ultimately lower conversion rates.

How does speed-to-lead affect staffing?

Research from InsideSales.com shows that leads contacted within 5 minutes are 8-10x more likely to convert than those contacted after 30 minutes. This means your service level target for inbound sales should be aggressive — 80% of calls answered within 30 seconds. Understaffing by even 1-2 reps during peak hours can significantly impact conversion rates.

Should I model SDRs and AEs separately?

Yes, if they handle different inbound queues. SDRs typically handle initial inbound qualification (shorter calls, higher volume), while AEs handle demo requests (longer calls, lower volume). Blending them in one Erlang C calculation will produce inaccurate results. Model each role as a separate queue.

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B2B SaaS Sales

SaaS Sales Team Staffing Calculator

Erlang C calculator adapted for B2B SaaS inbound sales. Plan staffing for demo requests, inbound leads, and customer success calls.

Start Calculating

Seasonal Planning:

Standard call volume — no seasonal adjustment applied

Call Center Parameters

Calls Per Hour40

Total incoming calls per hour across all lines

Average Handle Time (AHT)7m

Includes talk time + after-call work

Target Service Level80%

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

Target Answer Time30s

Maximum wait time in seconds. Standard: 20s

ShrinkageShrinkage accounts for breaks, training, meetings, sick time, and other non-productive time that reduces agent availability.35%

Typical range: 25-35%

Cost Per Agent Per Hour (optional)

Fully loaded cost for monthly cost estimate

Agents Needed

8 raw + 5 for shrinkage

Service Level

90.32%

Avg Speed of Answer

15.5s

Occupancy

58.33%

Probability of Wait

12.28%

Immediate Answer

87.72%

Traffic Intensity

4.67 Erlangs

Estimated Staffing Cost

Per Hour

$585

Per Month (160 hrs)

$93,600

B2B SaaS Sales Benchmarks

AHT Range

5m – 15m

Median: 7m

Service Level Standard

80/30

Occupancy Target

60-75%

Acceptable Abandonment

< 3%

Typical Shrinkage

30-40%

Source: Bridge Group SaaS Inside Sales Metrics, 2025

Call Center Staffing for B2B SaaS Sales

Inbound sales teams at SaaS companies face a different staffing challenge than traditional call centers. Call volume is lower, but each call represents significant potential revenue — a single demo call could convert to a $50K+ annual contract. The cost of a missed or slow-answered inbound lead is orders of magnitude higher than in transactional call centers.

Research consistently shows that responding to inbound leads within 5 minutes yields conversion rates 8-10x higher than waiting 30 minutes. For SaaS companies spending heavily on demand generation (Google Ads, content marketing, events), slow lead response effectively wastes acquisition spend. Understaffing your inbound sales team directly undermines your marketing ROI.

SaaS sales staffing also involves higher shrinkage than typical contact centers because reps spend significant time on non-call activities: CRM updates, pipeline reviews, team meetings, training on new product features, and administrative tasks. Effective use of Erlang C for SaaS teams requires honest shrinkage estimates — often 35-40% — to avoid chronic understaffing that leads to missed leads and rep burnout.

Key Challenges

•Each missed call represents potentially high-value pipeline ($10K-$500K+ ACV)
•Speed-to-lead is critical — response time within 5 minutes yields 8-10x better conversion
•High shrinkage (35-40%) due to CRM work, pipeline reviews, and training
•Calls vary dramatically: 5-minute qualification vs. 45-minute demo
•Q4 budget flush creates significant demand spikes

Common Call Types

Inbound demo requestsDiscovery and qualification callsProduct demo presentationsPricing and proposal discussionsTrial-to-paid conversion callsExpansion and upsell conversationsCustomer success check-ins

Staffing Tips

1Model inbound demo requests separately from outbound prospecting — they have completely different volume patterns and AHTs
2Target lead response time under 5 minutes — staff to ensure no inbound lead waits in queue during business hours
3Account for higher shrinkage (35-40%): SaaS reps spend more time in CRM, meetings, and training than transactional agents
4Consider lower occupancy targets (60-75%) — unlike support centers, sales reps need preparation time between calls
5Staff heavier on Tuesdays through Thursdays when inbound demo volume peaks; Monday and Friday are typically 20-30% lower

Compliance Note

GDPR and CCPA compliance for prospect data handling. Call recording requires consent notification in many jurisdictions. CAN-SPAM compliance for follow-up communications.

FAQ

B2B SaaS Sales Staffing FAQ

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