--- title: "What Is an Item Master?" url: https://www.uncap.com/glossary/item-master author: "Denis Dyli" published: 2026-10-14 updated: 2026-10-14 summary: "An item master is the central record an ERP or inventory system keeps for every item a business buys, makes, stocks or sells. Each record typically holds the item number, description, units of measure, cost, weight and purchasing settings, so purchasing, the warehouse, sales and finance can work from the same item data." --- # What Is an Item Master? > An item master is the central record an ERP or inventory system keeps for every item a business buys, makes, stocks or sells. Each record typically holds the item number, description, units of measure, cost, weight and purchasing settings, so purchasing, the warehouse, sales and finance can work from the same item data. **Item master**: An item master is the central record an ERP or inventory system keeps for every item a business buys, makes, stocks or sells. Each record typically holds the item number, description, units of measure, cost, weight and purchasing settings, so purchasing, the warehouse, sales and finance can work from the same item data. ## How it works In data management terms, an item master holds master data about products. Gartner defines master data as the least number of consistent and uniform sets of identifiers and extended attributes that uniquely describe the core entities of an enterprise and are used across multiple business processes, and products are one of the most common categories of master data. In practice, a purchase order, a pick ticket, an invoice and a web order can all refer to the same item record instead of retyping its details. Fields vary by system. Described in plain terms, an item record can cover groups like these: - Identity: the internal item number, a description, and any barcodes. GS1 US draws the line clearly: a GTIN is a universal, permanent number issued only by GS1 that every retailer, distributor or online marketplace uses for the product, while a SKU is a flexible code you create to track your own inventory. An item record can carry both. - Units of measure: how the item is stocked, bought and sold, and the conversions between them, such as a case of 10 boxes. - Physical data: weight and dimensions, which feed shipping and freight. - Cost and price: the item's cost and its base price. - Purchasing and planning: vendor, lead time, order quantities and reorder settings. - Classification and status: category, item class and whether the item is active. When other systems copy item data, they copy its mistakes too. Shopify, for example, uses product weight to calculate shipping rates, so a wrong weight synced from the item master becomes a wrong shipping rate. ## Item master vs. SKU vs. product listing An item master holds a full record for each item. A SKU is one field in that record, the code that identifies the item within your business. A product listing on a storefront is what a buyer sees, built from item master data plus selling content such as long descriptions and images, which can live in a PIM. ## Example A distributor's item master holds nitrile gloves under item number GLV-NIT-L. The base unit is a box, the item is bought by the case of 10 boxes and sold by the box. Cost is $6.00 a box, so a case costs 10 x $6.00 = $60.00. A box weighs 1.5 lb, so a case ships at 10 x 1.5 = 15 lb. In Shopify the variant gets SKU GLV-NIT-L, a cost per item of $6.00, a price of $9.50 and a weight of 1.5 lb. Using Shopify's margin formula, ([9.50 - 6.00] / 9.50) x 100 = 36.8 percent. If the cost changes in the item master and Shopify's cost per item is not updated, that margin no longer reflects the real cost. ## On Shopify In Shopify, the matching fields sit on the product and its variants, on the product details page: - SKU: an optional code that identifies the product within your business, and each SKU needs to be unique. - Barcodes: up to 20 per product or variant, typed as GTIN, UPC, EAN, ISBN, ASIN or Custom. - Cost per item: your cost, used to show profit and margin. - Weight: used to calculate shipping rates, so it needs to be exact. - Country or region of origin and HS code: for international shipping. - Vendor, product type and status: Active, Draft, Archived or Unlisted. Metafields extend Shopify's data model with your own custom data, for specialized information that isn't usually captured on product pages, such as part numbers. Shopify's ID metafield type exists to store the identifier of a resource in another system, such as an ERP's own item ID, and metafield definitions enforce validation rules so values stay consistent. ## How Uncap helps Uncap's [guide to ecommerce for manufacturers](/post/ecommerce-for-manufacturers) puts it plainly: an ERP item master was built to make and ship products, not to sell them. It can hold short codes, duplicate SKUs, discontinued items nobody removed and descriptions written for the warehouse. The guide's advice is to budget data cleanup as its own workstream, with an owner, before the storefront build starts. ## Related terms - SKU (stock keeping unit) - Master data management (MDM) - PIM (product information management) - GTIN (Global Trade Item Number) - Bill of materials (BOM) - System of record ## Sources - GS1 US: What is a GTIN? - Shopify Help Center: Product details page - Publication 538, Accounting Periods and Methods, IRS ## Frequently asked questions ### What is an item master? It is the ERP or inventory system's central record for each item a business buys, makes, stocks or sells. Purchasing, warehouse, sales and finance can all read the same record, so the item is described once. ### What are the items in inventory? The IRS says inventory should include merchandise or stock in trade, raw materials, work in process, finished products, and supplies that physically become a part of the item intended for sale. In an item master, each stocked item can have its own record.