Minimum level of stock

The minimum level of stock is a certain predetermined minimum quantity of raw materials or merchandise inventory which should always be available in stock in the normal course of business.

The minimum level of inventory is a kind of a precautionary level of inventory which indicates that the delivery of raw materials or merchandise may take more than the normal lead time. Lead time is the expected time taken by the supplier to deliver goods at the warehouse or at the point of consumption. If the level of stock strikes the minimum level, the management of the company must make sure that they corroborate with the supplier and take other necessary measures to make the goods (inventory or raw materials) available in time so that the business operations are not disturbed or delayed.

Formula:

The formulas used to calculate the minimum level of stock are given below:

Minimum Level of Inventory = (Maximum usage × Maximum lead time) – (Average usage × Average lead time)

Or

Minimum Level of inventory = Re-order level – (Average usage × Average lead time)

Both the formulas are equivalent and produce the same result.

Example 1

The Noor Clothing House sells T-shirts. Each shirt costs $15 and is sold for $20 to customers. The maximum demand is 20,000 shirts per year and the average demand is 18,570 shirts per year. The average lead time is 57 days and the maximum lead time is 64 days.

Required: Compute the reorder level and the minimum level of stock of T-shirts for Noor Clothing House.

Solution

• Maximum demand per day: 20,000 shirts/365 days = 55 shirts
• Average demand per day: 18,570 shirts/365 days = 51 shirts

Reorder level = (Maximum demand × Maximum lead time)
= (55 units × 64 days)
= 3,520 units

Minimum level of stock = Reorder level – (Average demand × average lead time)
= 3,520 units – (51 units × 57 days)
= 3,520 units – 2,907 units
= 613 units

Example 2

The Maham Autos deals in cars. The selected data is given below:

Annual demand:

• Maximum demand: 730 cars per year
• Normal or average demand: 365 cars per year
• Minimum demand: 283 cars per year

Lead time in days:

• Maximum lead time: 98 days
• Normal or average lead time: 87 days
• Minimum lead time: 73 days

Required: Compute minimum level of inventory for Maham Autos on the basis of above data.

Solution:

• Maximum demand per day: 730 cars/365 days = 2 cars per day
• Average demand per day: 365 cars/365 days = 1 car per day

Minimum level of inventory = (Maximum demand per day × Maximum lead time) – (Average demand per day × Average lead time)
= (2 units × 98 days) – (1 unit × 87 days)
= 196 units – 87 units
= 109 units

Example 3

A company makes iron tables. To manufacture one table, 2.35 kgs of iron (raw material) is used. The details are given below:

• Maximum demand for tables: 600 tables per month
• Average demand for tables: 475 tables per month
• Minimum demand for tables: 320 tables per month
• Maximum lead time: 2.5 weeks
• Average lead time: 1.9 weeks
• Minimum lead time: 1.5 weeks

Required: Compute the minimum kilograms of iron that the company needs to maintain.

Solution

• Maximum Usage: 600 tables × 2.35 kgs = 1,410 kgs
• Average Usage: 475 tables × 2.35 kgs = 1,116.25 kgs

Minimum level = (Maximum usage × Maximum lead time) – (Average usage × Average lead time)

= (1,410 kgs × 2.5 days) – (1,116.25 kgs × 1.9 days)
= 3,525 kgs – 2,121 kgs
= 1,404 kgs