How to calculate total hours an order took to complete it?

"We want a report that gives us order-wise total labor hours spent to complete the whole order", asked one of my contacts.

I asked, “Why do you need this kind of report?’

They shared the purpose of developing this report – ‘Order-wise total worked hours.'

1. To compare the projected working works to complete an order and the actual hours worked to complete the order by the production lines.

2. This comparison would help to know how much extra cost is incurred in making an order. The labor cost is estimated before moving the order in a line vs actual expenses on the order.

3. The variation ratio would be used in calculating labor cost in future orders with better accuracy

4. Another important purpose of this is industrial engineers who estimate projected order completion hours, can improve their projection by looking into the variation of their current estimates and considering the different variables of order completion.

How to make the report for total hours worked by orders

The report can be developed easily if the factory keeps their daily manpower record by style and by a line and daily working hours. Records of OT working hours (if applicable). 

You can generate this report from your daily production report (DPR) if you have a style-wise manpower headcount in your DPR.

If you know the production start date and production completion date of an order, you can calculate the total hours worked for an order using the following method. Let’s say on the first day and last day partial manpower was utilized for the said order.

First day hour worked (A) = Manpower x hours worked
Last day hours worked (B)= Manpower x hours worked
Total hours worked on the other day (C)= Manpower x 8 x Number of days
Order wise total hours = A+B+C

Total hours worked by order

An example: 
Let's say a 30 workstations line is used to make an order (Style#123) of 2000 pieces. It took total 8 days to complete the order for 30 operators. On the first day, 20 operators worked for average 4 hours on this order and on the last day 15 operators worked for average 5 hours. Other days six days all 30 operators were present and the whole day they worked on this style only. 

Threfor calculate total hours worked on this order
= (20 x 4)+ (30 x 8 x 6) + (15x5) Hours 
= (80 + 1440 +75) Hours 
= 1595 Hours

Variable in establishing a formula for calculating total hours worked

But there are a couple of variables in using the above formula. On the floor, all numbers are not in round figures. You will have the following situation everyday work.
  1. Many operators will not be working a full day (8 hours) on the same order
  2. Many operators in a line will have no work (idle time) all day and many loss time hours will be there every day. Do you like to include all these idle hours? From the cost perspective, yes, you should. But from the performance perspective, you should not.
  3. Operators will be moved from one line to another (one order to another order)
  4. Few operators will be helping on the said order to build up WIP or complete the high WIP. Can you keep a record for this dynamic nature of workers' movement in the production lines?
  5. You will have absentees in some days and some other days line will not perform well.

Manually preparing daily records with all these variables is not practical. Then how one can make such a report and get complete working hours on the orders? 

The good news is that the contact who asked me this question has a real-time production tracking system that keeps the record of bundle worked time for all bundles of order by operation and by operators who worked on the order. They have daily attended hours by operators as well. 
As they had all these records in the database, it become easier to make their report even after considering a few variables. 

Conclusion:
I hope you understand the variables in need to be considered in calculating the total hours an order takes to complete. This report can be prepared by all the garment manufacturers after order completion. They can compare the planned hours for order and actual hours incurred to complete their orders.