SKU Generator

What is a SKU, exactly?

A Stock Keeping Unit is the smallest unit of a product that your business tracks separately in stock. If you sell a hoodie in three sizes and two colours, that is six SKUs, not one — each combination needs its own code because each is ordered, stocked and sold independently. The SKU is entirely internal: unlike a barcode, no external body issues it or checks it for uniqueness. You are free to build whatever format suits your operation, as long as it stays consistent and unique across your own catalogue.

Retailers in the UK typically build a SKU from three to five short segments — category, brand or supplier, a size or variant code, a colour code, and sometimes a sequential number — joined by hyphens. The result usually sits between 6 and 15 characters: long enough to be meaningful, short enough to read on a shelf label or a packing slip at a glance.

SKU vs EAN, UPC, GTIN, serial and batch numbers

These terms get mixed up constantly, and the confusion causes real stock-control mistakes, so it is worth being precise. An EAN (European Article Number, the UK and EU standard, part of the wider GTIN family) is a globally unique barcode number issued through GS1 UK. It identifies a product to every retailer and supplier on the planet — Tesco, Amazon and a corner shop all read the same EAN as the same item. You cannot make one up; GS1 licenses company prefixes and you assign numbers within your own block.

A SKU has none of that infrastructure. You invent it, it only has to be unique inside your own systems, and it can (and often should) encode information the EAN never will — which supplier you bought it from, which season it belongs to, or where it sits in your own category tree. Amazon and eBay call your SKU the "seller SKU" or "custom label" precisely because it is yours to define, layered on top of their own listing ID and any EAN/UPC the product carries.

Serial numbers are different again: they identify one individual unit (useful for electronics, tools and anything under warranty), while a batch or lot number identifies a production run (essential for food, cosmetics and anything with a use-by date or recall risk). A SKU sits above both — one SKU can cover thousands of units across many batches and serial numbers.

Step-by-step: designing your own SKU naming convention

Worked example for a small UK clothing retailer: category "Hoodie" → HOO, brand "Nova" → NOV, size "Medium" → M, colour "Charcoal" → CHR, giving HOO-NOV-M-CHR. Add a two-digit batch suffix if you restock the same combination from a different supplier later — HOO-NOV-M-CHR-02.

1. List the attributes that actually help you find stock fast. For most shops that is category, brand or supplier, size, and colour — resist the urge to add more than four or five, or the code becomes unreadable.
2. Decide an abbreviation rule per attribute. "Hoodie" might become "HOO" (first three letters), "Extra Large" might become "XL" (an initials rule), and a colour list might use a fixed custom mapping so "Charcoal" always shortens to "CHR", never "CHA" one week and "CHR" the next.
3. Pick one separator and stick to it. A hyphen is the safest universal choice — it survives copy-paste into Excel, Shopify, and most marketplace bulk-upload templates without being reinterpreted as a formula or a date.
4. Add a sequential number if two products could otherwise collide — e.g. two different suppliers both selling a "blue medium hoodie" under your own abbreviation scheme. Zero-pad it (001, 002…) so the codes sort correctly in a spreadsheet.
5. Decide on a maximum length before you generate anything. Marketplace fields have hard limits (see below), and a 40-character SKU is not more informative than a 14-character one — it is just harder to read on a shelf.

Best practices — and the mistakes that come back to bite you

• Avoid the letter O and the digit 0 together, and the letter I or lowercase l next to the digit 1 — on a printed label or read aloud over a warehouse radio, these are genuinely hard to tell apart. This generator flags both automatically.
• Never start a SKU with a zero. Excel and Google Sheets silently strip leading zeros when a cell is treated as a number, turning "007-BLU" into "7-BLU" the moment someone re-opens your export. The tool exports SKUs as text specifically to avoid this, but it is still worth avoiding a leading zero in the design itself.
• Don't encode information that changes — a supplier's cost price, a warehouse shelf location, or a promotional price. All three change independently of the product itself, and re-issuing SKUs every time a supplier changes is far more disruptive than the small win of having that detail baked in.
• Keep the format identical across your whole catalogue. A SKU scheme that's 8 characters for shoes and 14 for accessories looks fine until you try to sort or filter a spreadsheet by SKU and the columns don't line up.
• Stick to A–Z, 0–9, hyphens, underscores and full stops. Spaces, slashes, ampersands and accented characters cause silent failures in CSV imports on Shopify, WooCommerce and most marketplace bulk tools.

Marketplace-specific SKU rules for UK sellers

Amazon Seller Central (UK): the "Seller SKU" field allows up to 40 characters, but Amazon strongly recommends avoiding characters outside letters, numbers and hyphens — special characters have historically caused listing feed errors. Once a SKU is attached to a listing with sales history, Amazon discourages reusing it for a different product even after the original is discontinued.

eBay UK: the equivalent field is the "Custom Label", limited to 50 characters, used purely for your own inventory management — it never appears to buyers. It is the ideal place to drop your full internal SKU even if your public listing title is entirely different.

Not On The High Street, OnBuy and most smaller UK marketplaces: typically accept whatever SKU format you already use in your existing inventory system and import it as-is via CSV, which is exactly the export format this tool produces.

Whichever platform you sell on, GS1 UK remains the authority for the EAN/barcode side of your product data — the SKU and the EAN are complementary, not competing, identifiers, and most marketplace listing templates ask for both.

Bulk workflow: from spreadsheet chaos to a clean variant matrix

The single biggest time cost in SKU management is entering size/colour combinations one at a time. If you stock 4 sizes and 5 colours across 3 styles, that's 60 SKUs — manageable in this tool in under a minute, because entering "S, M, L, XL" once against the Size attribute and all five colour names once against Colour generates every combination automatically as a true cartesian matrix, not a queue of single-item forms.

Once generated, sort the results table by any column to spot-check a size run, copy the whole set to your clipboard for a quick paste into an email, or export to CSV or Excel. The Excel export writes every SKU as text, not a number, so codes with leading digits or hyphens import into your inventory system, Shopify, or a marketplace bulk-upload template exactly as generated — nothing gets silently reformatted.