How to Size WhatsApp Service Shifts Based on When Messages Arrive

How to size WhatsApp support shifts based on the time messages arrive

If you run a business on WhatsApp, at some point you will ask yourself how many people you need per shift to avoid leaving messages unanswered. The answer is not a magic number: it depends on how many messages arrive, at what times, and how long it takes you to respond to each one. This article gives you the method to calculate it with your own data and a reference table you can use as a starting point.

The most common mistake is sizing by the daily average. If you receive 300 messages spread evenly in a day, one person is enough. But if 80% arrive between 12:00 and 14:00, you need three people during that time and only one the rest of the day. The average hides the peaks, and the peaks are what determine how many people you need.

What data you need to calculate it

Before doing any math, you need to have three numbers per shift or time slot:

• Volume of incoming messages per slot: how many messages you receive in each one- or two-hour block. You get this from the WhatsApp Business history or from the inbox of your management tool.
• Average response time per message: how long it takes a person to respond to a message from start to finish, including reading, thinking, and writing. If you have not measured it, start with 3 minutes as a conservative value and adjust it later.
• Productive hours per shift: how many effective hours a person works in the shift, discounting breaks, meetings, and moments without messages. An 8-hour shift usually has 6.5 or 7 productive hours.

The basic formula

The formula to know how many people you need in a time slot is simple:

People needed = (messages in the slot × average time per message) / (productive minutes in the slot)

The result is always rounded up. If it gives you 1.2 people, you need 2. The fraction indicates that one person is not enough, not that there is half a person.

Quick reference table

The following table gives you the number of people needed for different combinations of volume per hour and average response time, assuming a productive hour of 50 minutes (that is, 10 minutes of break per hour). It is a starting point: adjust it with your own times.

Read the table like this: if you receive 40 messages in an hour and each response takes you 3 minutes, you need 3 people in that hour. With 2 people, one alone would have to answer 20 messages per hour, which gives 60 minutes of work: right at the limit, with no margin for unforeseen events.

How to apply the table to your shifts

1. 1Divide your day into one-hour slots and note how many incoming messages you receive in each one. Use data from at least two weeks so that a rare day doesn't distort your count.
2. 2Measure your average response time: time ten responses and take the average. If you can't measure it, use 3 minutes as the initial value.
3. 3Look in the table for the row of your volume per hour and the column of your response time. The number where they intersect is the number of people you need in that slot.
4. 4Add up the needs of all slots in a shift and compare them with the people you have. If one slot needs 3 and another 1, you can move breaks or tasks to balance them.
5. 5Check the result against your real productive hours: if your shift has more breaks than the 10 minutes per hour we assumed, add one person or reduce the expected volume.

Applied example: a dental clinic

A clinic receives on average these messages per hour, according to its WhatsApp history:

In total, the clinic needs the equivalent of 15 person-hours distributed throughout the day, but the peak from 12:00 to 13:00 requires 3 people at the same time. With 2 fixed people plus one covering noon, or by moving the break of one of the fixed people to another slot, it's enough. If they sized by the daily average (25 messages per hour), they would say 2 people are enough, and they would be wrong at the peak.

Frequent errors when sizing

• Using the daily average instead of the hourly distribution: it's the most expensive error. The average hides peaks and leaves you without coverage just when most messages arrive.
• Not deducting breaks: if a person works 8 hours but takes 30 minutes for lunch and two 10-minute breaks, their productive hours are 7.1, not 8. Sizing with gross hours leaves you short.
• Rounding down: if the calculation gives 1.8 people, rounding to 1 is an invitation for messages to pile up unanswered. Always round up.
• Not considering messages that require forwarding: if a message has to go to another department, the real response time is longer. Add the forwarding time to the average time.
• Sizing only once a year: message volume changes with seasonality, campaigns, and business growth. Review the sizing every quarter.

How to adjust the calculation when messages are not even

The table assumes that messages arrive distributed more or less evenly within the hour. In practice, there are micro-peaks: for example, if a mass message goes out at 10 in the morning, messages may concentrate in the first 15 minutes of that hour. In that case, the table underestimates the need.

For those scenarios, you have two options. The first is to use a shorter time slot for the calculation: instead of an hour, use 15- or 30-minute blocks during times you know are critical. The second is to add a 20% safety margin to the table result when you know there are active campaigns or specific high-volume days.

The safety margin is not optional if your business depends on responding quickly. A message that waits 40 minutes during peak hours could be a patient who goes to another clinic or an order that is lost. Better to have someone with secondary tasks than to lose sales.

What to do if you don't have enough staff

If the calculation tells you that you need more people than you have, hiring isn't the only solution. First, review these levers:

• Reduce average response time: templates for frequent responses, WhatsApp Business quick replies, or a tool with AI suggestions like Wando can lower the time per message from 3 to 2 minutes, which reduces the number of people needed in the table.
• Shift business hours: if the peak is from 12:00 to 13:00, you can move one person's shift to start at 11:00 to cover the peak, instead of having everyone start at 9:00.
• Route simple messages to a chatbot or auto-response: frequent queries like hours or address can be resolved without human intervention, freeing up time for those that do require it.
• Balance the load: if one time slot has 3 people and another has 1, move breaks or administrative tasks so that people are available during the peak.

Conclusion

Sizing WhatsApp service shifts is a calculation done with data, not intuition. You need to know how many messages arrive per hour, how long each response takes, and how many productive hours each person has. With those three numbers, the table in this article gives you a reliable starting point. The daily average will lead you to an error: use the hourly distribution.

What to do when the peak exceeds your maximum capacity

Sometimes the calculation gives you an impossible number to cover, like 6 people in a time slot when your business has 3. In that case, it's not enough to move breaks around: you have to change the game. The first option is to reduce the peak: if 80% of messages arrive in one hour, you can publish narrower service hours or use a WhatsApp campaign to anticipate queries and spread them throughout the day. The second is to accept that something will have to wait and prioritize: sales or urgent messages first, the rest with an auto-response that notifies the delay time.

How to size with tools that measure for you

If you use Wando, the statistics report gives you the volume of messages per hour and per day without having to count by hand. That saves you the most tedious step of the calculation. Additionally, you can use the response time that the tool itself records to fine-tune the table with real data, instead of the estimated value of 3 minutes. With those two numbers, sizing becomes a spreadsheet that updates itself every month.

Uncomfortable questions no one answers

• What if a message requires research? The average time of 3 minutes assumes direct responses. If part of your messages involves looking up info in a system, add that time to the average or assign that task to a more experienced person.
• What about messages that arrive outside business hours? Don't count them for shift sizing, but do count them to decide whether to activate auto-responses or an agent to process them first thing in the morning.
• What if the volume is so low that one person is more than enough? The minimum sizing is 1 person per shift, even if the formula gives 0.3. Idle time is the cost of being available.
• What if the table tells me I need 10 people and that's unfeasible? Check if you can lower the time per message with templates or AI. Going from 4 to 2 minutes per message halves the need.