A SKU, or stock keeping unit, is an internal code that identifies one specific product and variation. A clear SKU system helps you find stock, update listings, create purchase orders and understand which items are actually selling.
Your SKU does not need to be clever. It needs to be consistent, unique and easy for a human to read without opening a spreadsheet every time.
What makes a good SKU?
A practical SKU should be:
- Unique: one code points to one sellable product variation.
- Consistent: the same structure is used across your catalogue.
- Readable: staff can understand the important parts at a glance.
- Stable: the code does not change just because the price or supplier changes.
- System-friendly: it avoids confusing characters and works in CSV imports.
Keep SKUs separate from marketplace-generated IDs, barcodes and supplier part numbers. You can store all of them in your product record, but they serve different purposes.
A simple SKU format
Start with three or four meaningful sections separated by hyphens:
CATEGORY - PRODUCT - VARIANT - SIZE
For example, MUG-CER-BLU-350 could represent a blue 350 ml ceramic mug. A clothing example might be TEE-CLS-BLK-M for a classic black T-shirt in medium.
Use abbreviations that your team can understand. If “BLK” means black, do not later use “BK” for another black product. Write your abbreviation rules in a short reference sheet.
Choose what belongs in the code
Include attributes that help you identify and pick the correct item:
- Product family or category
- Model or product line
- Colour, material or flavour
- Size, pack count or capacity
- Version when two versions must be stocked separately
Do not add information that changes frequently, such as price, supplier cost, storage shelf or promotion. Those fields belong in your inventory data, not in the permanent identity of the product.
When should variations have different SKUs?
Give each variation its own SKU when it is picked, packed, counted or reordered separately. A T-shirt in three sizes and two colours needs six SKUs if each combination is a separate stock item.
Multipacks also need their own SKU when the pack is sold as a different unit. For example, a single candle and a three-pack may use CND-VAN-001 and CND-VAN-3PK. This prevents one product’s stock count from being confused with another’s.
Numbers, letters and leading zeroes
Letters make categories easier to scan, while numbers work well for sequential product families. If you use numbers, choose a fixed length such as 001, 002 and 003. This keeps sorting predictable.
Be careful with spreadsheet software: codes such as 0012 can be converted to 12 if the column is treated as a number. Store SKUs as text and check the file after export. Before importing a listing file, use the CSV Cleaner & Viewer to look for missing values, broken columns and accidental formatting changes.
Characters to avoid
Avoid spaces, slashes, emojis and punctuation that may be interpreted differently by marketplaces. Do not use characters that are easy to confuse, such as zero and the letter O, or one and the letter I, unless your system makes the difference obvious.
Hyphens are usually easier to read than long unbroken codes. Keep the overall length reasonable so staff can enter it accurately on a phone or packing station.
How to build a SKU system from existing products
- Export your current catalogue and make a master list.
- Separate products from variations and multipacks.
- Decide your category and attribute abbreviations.
- Assign one permanent code to every sellable stock item.
- Check for duplicate codes and blank codes.
- Save the mapping between old identifiers and new SKUs.
- Update listings, bins, purchase records and picking sheets together.
Do not rename products halfway through a stocktake without keeping the old-to-new mapping. A clean transition is more important than a perfect-looking code.
SKU mistakes that cause inventory problems
Using the same SKU for different variations
If red and blue products share a code, sales and stock counts become unreliable. Make the variation part of the SKU when the items are physically different.
Embedding the selling price
A price-based SKU becomes misleading after a sale, currency change or supplier increase. Keep price in a separate field.
Changing codes after every supplier update
If the item is still the same product, keep the SKU stable and record the supplier change separately. Create a new SKU only when the product or customer-facing variation is materially different.
Making codes too descriptive
A SKU is an identifier, not a full product description. Long codes create typing errors and make fulfilment slower.
Connect SKUs to reorder decisions
Once every variation has a reliable SKU, you can measure sales and stock at the right level. A popular product in one colour may need reordering while another colour sits untouched.
Use the Inventory Reorder Point Calculator to estimate when a specific SKU should be reordered. Include average daily sales, supplier lead time and a safety buffer. For pricing decisions, the Profit Margin Calculator helps compare the profit of each product after selling costs.
Final checklist
- Every sellable variation has one unique SKU.
- The format is documented and used consistently.
- Codes do not contain price or temporary information.
- SKUs are stored as text in spreadsheets.
- Marketplace IDs and supplier codes are kept in separate fields.
- Old and new codes are mapped during a migration.
- Stock, sales and reorder reports use the same SKU.
A good SKU system is deliberately boring. That is a strength. When a product needs picking, counting, reordering or investigating, the right code should make the answer faster and reduce avoidable mistakes.