Glossary

Service level (SL)

Service level (SL) is the share of offered calls answered within a target time. It is written as X/Y: 80/20 means 80% of calls are answered within the first 20 seconds. This target is used to work out how many agents the line needs.

Why it mattersThe key measure of line availability – it tells you whether you have enough agents.

Also called: SL, Service level target, Telephone service factor (TSF), 80/20

FormulaSL = calls answered within time T / calls offered × 100%T is the target time, e.g. 20 seconds. Calls offered = answered + abandoned. Short abandons – for example, calls dropped within the first 5 seconds – can be left out of the count entirely.

Example

Formula and example

In one hour 400 calls reached the queue and 336 of them were answered within the first 20 seconds. SL = 336 / 400 × 100% = 84%, so the 80/20 target is met for that hour. The other 64 calls were answered later or abandoned – they still count in the denominator.

Teams treat abandoned calls differently. If you exclude short abandons, do it the same way for service level and for abandonment rate, and state the method in the report.

Metrics

Typical targets

There is no single right target – it depends on the purpose of the line and the channel.

80/20The classic target for inbound calls in sales and customer service.

90/10Where speed matters: emergency and premium lines.

70/60 or looserBack-office and non-urgent questions.

Chat and emailMeasured in minutes and hours: for example, 80% of chats in 60 seconds, email replies within 4 hours.

How it works

Why it is measured by interval

Service level depends on three things: volume, average handle time, and the number of agents on the line at each moment. So it is read per 15- or 30-minute interval. A daily average of 85% can hide a 10:00-11:00 AM hour at 60%, when callers waited for minutes.

Worked example: 100 calls of 180 seconds arrive in half an hour – that is 10 erlangs. By the Erlang C formula, 13 agents answer 79.6% of callers within 20 seconds and 14 agents answer 88.8%. An 80/20 target needs 14 agents on the line, and with 30% shrinkage, you need to plan for 20 people.

Practice

How to meet the target

Forecast volume by interval and schedule people to match it
Allow for shrinkage: breaks, training, and absences
At peaks, bring in an overflow group and offer callers a callback
Hand simple questions to the IVR, chatbots, and AI voice agents
Watch service level on a live dashboard and react before the interval ends

In CONTACT.WORK

How it works in CONTACT.WORK

Live dashboards show service level, queues, and waiting callers right now, and reports give the picture by day, channel, and team. The workforce management module forecasts calls and chats by hour and calculates how many agents you need to hit your service level target.