Call center KPI glossary: metrics defined with formulas

This call center KPI glossary defines the metrics people use to run sales and support calling, with a formula for each and a note on what to watch for. Definitions vary between teams, so the most important habit is to write down yours, including the denominator, and keep it the same over time.

For which metrics to prioritise, read AI calling metrics that matter. Use this page as the reference behind it.

How to use this glossary

• Pick five to eight metrics, not all of them.
• Write each definition and denominator in your own team doc.
• Compare periods using the same definition.
• Pair a volume metric with a quality metric so neither is gamed.

Reach and connection metrics

Metric	Formula	Notes
Dials	Total call attempts	Volume only, says nothing about quality
Answer rate	Calls answered by a person / dials	Decide whether voicemail counts; most teams exclude it
Contact rate	Leads reached at least once / leads called	Lead-level, not call-level
Not-reached rate	Leads never answered / leads called	Your list for text and email follow-up
Voicemail rate	Calls ending in voicemail / dials	High rates can suggest poor timing
Attempts per lead	Dials / unique leads	Compare with your cadence plan
Abandonment rate	Inbound calls dropped before answer / inbound calls	Lower is better; watch peak hours
Bad number rate	Invalid or disconnected numbers / dials	Points to list quality problems

Conversation metrics

Metric	Formula	Notes
Conversation rate	Calls above a minimum length (for example 30 seconds) / answered calls	Filters out hang-ups
Average talk time	Total talk time / calls	Longer is not always better
Average handle time (AHT)	(Talk time + hold + wrap-up) / calls	Staffing metric
Hold time	Total time on hold / calls placed on hold	Mainly inbound
Interruption rate	Calls where the caller interrupted / calls	Useful for AI agents; reveals pacing issues
Transfer rate	Calls transferred to a human / conversations	For hybrid setups
Hang-up in first 10 seconds	Calls ended within 10s / answered calls	Tests your opening line

Outcome metrics

Metric	Formula	Notes
Qualified rate	Qualified leads / conversations	Define "qualified" in writing
Booked rate	Meetings booked / conversations (or / leads, state which)	Core sales metric
Show rate	Meetings attended / meetings booked	Low show rate often points to weak confirmation
No-show rate	1 minus show rate	Pair with reminder tests
Conversion rate	Leads that reached a defined goal / leads in the group	Always name the goal and group
Callback rate	Callbacks requested / conversations	Signals interest or bad timing
Opt-out rate	Do-not-contact requests / leads called	Watch for spikes after list changes

Speed metrics

Metric	Formula	Notes
Speed to lead	First call time minus lead arrival time	Use the median
Average speed of answer (ASA)	Total wait before answer / answered calls	Inbound
Service level	Calls answered within a target time / calls offered	For example, answered within 20 seconds
First-call resolution	Issues solved on first contact / issues	Support metric

For the operating model behind speed, see the speed to lead playbook.

Cost and efficiency metrics

Metric	Formula	Notes
Cost per call	Total calling cost / calls	Include provider and software costs
Cost per conversation	Total cost / conversations	Better than cost per dial
Cost per booked meeting	Total cost / meetings booked	See the cost per booked meeting calculator
Cost per qualified lead	Total cost / qualified leads	Useful before the meeting stage
Calls per rep per day	Dials / rep days	Capacity measure, not performance
Utilisation	Time on calls / available time	Staffing only

Quality metrics

Metric	Formula	Notes
Quality score	Points earned on a rubric / points possible	See the call quality scorecard
Compliance pass rate	Calls meeting all required items / calls reviewed	Review a sample every week
Unanswered question rate	Calls where the agent could not answer / calls reviewed	Feeds your knowledge base
CSAT	Satisfied responses / survey responses	Needs a survey step

Worked example (illustrative)

A team dials 1,000 leads in a week. 280 answer, 210 hold a conversation of over 30 seconds, 60 are qualified and 30 book a meeting. Total cost for the week is [£/$] 900.

• Answer rate: 280 / 1,000 = 28 percent
• Conversation rate: 210 / 280 = 75 percent
• Qualified rate: 60 / 210 = about 29 percent
• Booked rate: 30 / 210 = about 14 percent
• Cost per booked meeting: 900 / 30 = 30

The numbers are invented to show how the metrics chain. Your funnel will differ.

Common mistakes with KPIs

1. Using different denominators in different reports.
2. Tracking dials but not outcomes.
3. Averaging response times when the median tells the truth.
4. Cutting handle time and losing conversations.
5. Counting voicemail as a conversation.

Try it

Purple Voice shows calls, transcripts, summaries and recordings in the dashboard, with campaign progress and not-reached analytics; Pro adds Insights. The Free plan lets you start tracking with no card, at voice.purplerocket.co.