Units of Measurement

The Stock -> Stock settings -> Units of measurement section contains a list of all main units of measurement (UoM) used in stock.

From this page, it is possible to add new units of measurement and edit existing units, which are used in stock.

Additionally, in MRPeasy it is possible to:

  1. define unit conversions for more comfortable use in BOMs (e.g. kg -> g, lbs -> oz),
  2. define conversions from vendor's units of measurement to stock units (e.g. 1 package on PO -> 30 pcs in stock).

For example:

  1. You track an item in your inventory in pounds.
  2. A vendor sells items in "bags", where each bag is 12 lbs. Your PO to the vendor shows that you are ordering a number of bags. This is a vendor-specific UoM conversion.
  3. When a bag is received, inventory increases by 12 lbs. 
  4. You use this item in a product in ounces. In a bill of materials (and later MO), the quantity to consume is e.g. 1 oz per product. This is a unit conversion from the main unit.

What is a unit of measurement?

A unit measurement defines in which units you count something in stock.

For example:

  1. various parts, discrete objects are counted in pieces. The unit of measurement is typically abbreviated as "pcs" for pieces, or "ea" for each.
  2. liquids are measured by volume. The unit of measurement may be "l" for liters, "fl oz" for fluid ounces, etc. Even though liquids could be bought in containers by piece, these must be converted to the actual volume for accurate stock-keeping purposes.
  3. dry goods, powders, or raw metal is usually measured by weight. The unit of measurement may be "kg" for kilogram, "t" for tonne, or "lbs" for pounds, etc.
  4. other raw materials which come on rolls, typically fabric or sheet metal, are measured in length or area. The unit of measurement may be "m" for meters, "ft" for feet, etc. In some setups, these might also be measured in square meters "m^2" or square feet "sq ft", or even by weight.

Nowadays, there are three widespread systems of units of measurement:

  1. The metric system, also known as the SI (Système Internationale) system, is used in most parts of the world. For example, the base unit for weight is kilogram "kg", and for length is meter "m", and where a conversion of a unit is always a power of ten, e.g. kilometer = 10^3 meters.
  2. The imperial system used in the UK and some former British colonies.
  3. The United States Customary Units (USC) used in the US. This system originates from the imperial system, but some units are defined differently, the same units represent different absolute quantities. Some common units in both of these systems are pounds "lbs" to measure weight and feet "ft" to measure length. Conversions between units are more complicated compared to the SI system due to being a matter of tradition in these systems, e.g. 1 mile = 5280 feet or 1760 yards, 1 yard = 3 feet, 1 foot = 12 inches.

One company should not mix up the usage of the metric system, the imperial system, and the US customary units, if at all possible. This is bound to bring misunderstandings between workers, and perhaps even with your customers or vendors. When using the imperial system, there might be a need to be explicit if it's the US or the British system, e.g. when you're in the US and ordering from the UK or vice versa.

On the international market, it is best to use the metric system. (NASA lost a $125 million Mars orbiter because one engineering team used English units of measurement while another team used the metric system. Long story short, it crashed on Mars.)

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