what is a man-day

What are man days in quality inspections, and how to calculate it?

Quality inspections ensure that your products meet the standards and specifications that the brand and customers expect. An inspection can be performed at different stages of the production process, such as pre-production, during production, pre-shipment, or after delivery. 

A key factor determining the cost and duration of a quality inspection is the man-day. So what are man days, and how to calculate it for your inspection requirements?

What is a man-day?

man days in quality control

In quality control, a man-day is a unit of measurement that represents the amount of work that one inspector can perform in one day. A man-day is typically calculated based on an 8-hour working day, excluding breaks and travel time.

What are the factors that affect man-days?

Many factors affect the number of man-days required for a quality inspection. Those factors are:

Sampling size

This is the number of units or samples that must be inspected from a given lot or batch of products. The sampling size can be determined using statistical methods, such as the AQL (Acceptable Quality Level) standard, which defines the maximum number of defects acceptable for a given sample size and inspection level.

Inspection criteria

This list of checkpoints or requirements must be verified during the inspection. The inspection criteria include functionality, appearance, dimensions, labeling, packaging, safety, and compliance. The buyer, the supplier, or a third-party standard can define the inspection criteria.

Inspection complexity

The difficulty or detail level involved in the inspection also affects man-day calculation. The inspection complexity can depend on the nature of the product, the inspection method, the equipment or tools required, and the inspector’s skills and experience.

Inspection location

Where the inspection takes place, such as the factory, warehouse, port, or customer’s site, also affects the man-day calculation because the location can affect the travel time, transportation costs, and accessibility of the inspector.

How to calculate the number of man-days for an inspection?

To calculate the number of man-days required for a quality inspection, you need to estimate the time needed for each of the above factors.

For example, let’s say you want to inspect 500 units of a product with 10 checkpoints at a factory 2 hours away from your inspector’s office. You can use the following formula:

Man-days = (Sampling size x Inspection time per unit + Travel time per day) / Working hours per day
  • Sampling size = 500
  • Inspecton time per unit = 5 mins
  • Working hours per day = 8 hours = 8 x 60 mins = 480 mins
  • Travel time per day = 2 hours to factory + 2 hours go back to inspector’s office = 2 + 2 = 4 hours
So we get:
  • Man-days = (500 x 5 + 4 x 60) / (8 x 60)
  • Man-days = 5.70

You need about 6 man-days to complete the inspection.

Why is man-day important for quality inspections?

As a buyer or quality inspector, it is important to understand and estimate the man-day required for a quality inspection because it helps the business owner plan and budget their quality control activities and resources. They can also use the calculation to negotiate and compare the prices or services of different inspection providers or agencies, then improve competitiveness. Another benefit is that they can evaluate the performance and efficiency of inspectors. Lastly, understanding man-day can help better communicate with suppliers or customers about the inspection schedule and expectations.

How to optimize the man-day for quality inspections?

There are ways to optimize the man-day for quality inspections and reduce costs and time without compromising quality standards. Here are the tips for consideration:

Choose an appropriate sampling size and inspection level 

Based on your product type, quality requirements, and risk tolerance, you can use statistical tools or consult with industry experts to determine the optimal sampling plan for your case.

Define clear and realistic inspection criteria that cover all the essential aspects of your product quality.

A checklist or template to standardize your inspection process and avoid confusion or ambiguity will greatly help.

Select qualified and experienced inspectors

You want to work with professionals with the necessary skills, knowledge, and equipment to perform the inspection effectively and efficiently.

Coordinate with your suppliers and inspection providers to arrange the inspection at a convenient time and location

You can save much more by minimizing travel time and transportation costs. Also, request the inspectors to prepare the products and documents in advance to facilitate the inspection process.

Conclusion: What are man days in quality inspections, and how to calculate it?

Understanding man-days is essential for businesses engaged in sourcing and quality control. By following the tips above, buyers or QC providers can optimize the man-day for quality inspections and ensure that the products meet expectations and satisfy the customers. 

A man-day may affect total inspection fee. Learn more here.

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