Unit of measure
A unit of measure is the unit a number is counted in, such as kg, g, cm, mm or ml, and without it the number cannot be read correctly.
- UOM
What it means
A number without its unit is not a measurement. “2500” is a sensible weight for a kettle in grams, and two and a half tonnes in kilograms. Supplier files drop the unit, misspell it, or mix several in one column: 2.5kg, 2500 g, 2,5 KG and 5.5 lb, all in one Weight column.
The fix is one number per cell and one unit per column, named in the header: “Weight (kg)”, not “Weight”. Write each unit as its symbol, kg rather than KG or Kgs. In the SI conventions NPL publishes, a symbol stays in lower case unless the unit is named after a person. They also say: “Unit symbols are unaltered in the plural.”1
For a UK catalogue, use metric. GOV.UK says “You must use metric measurements (grams, kilograms, millilitres or litres) when selling packaged or loose goods in England, Scotland or Wales”, and Northern Ireland has different rules.2
Think of it like this
A unit of measure is like the currency sign on a price. 20 means nothing until you know whether it is pounds, euros or yen, and adding pounds to euros gives a wrong answer.
For example
Five kettles arrive weighing “2.5kg”, “2500 g”, “2,5 KG”, “5.5 lb” and “approx 2.5”. In a Weight (kg) column the first four become 2.5, 2.5, 2.5 and 2.49, using the pound’s legal definition of 0.45359237 kg.3 The fifth is flagged, because “approx” is a hedge where its unit should be.
Why it matters
Each channel reads units differently. Google wants the unit in the cell, as in 3 kg.4 Shopify wants whole grams with no unit.5 WooCommerce wants a bare number in the store’s own unit.6 Mixed units fail without an error message, and a store set to kilograms that imports grams records each product at a thousand times its weight.
Not to be confused with
In a supplier’s price list, a column headed UOM may mean the selling unit instead: each, pack or case. Read a trade price per case as a price per item and the cost of every item is wrong.
Sources
- NPL (National Physical Laboratory). SI units.
- GOV.UK. Weights and measures: the law: Units of measurement.
- legislation.gov.uk. Weights and Measures Act 1985, Schedule 1: Definitions of Units of Measurement.
- Google Merchant Center Help. Delivery weight [shipping_weight].
- Shopify Help Center. Using CSV files to import and export products.
- WooCommerce documentation. Products Settings.