SKU Generator

What is a SKU number, exactly?

A Stock Keeping Unit is the smallest unit of a product that your business tracks separately in inventory. If you sell a hoodie in three sizes and two colors, that's 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're free to build whatever format suits your operation, as long as it stays consistent and unique across your own catalog.

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

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

These terms get mixed up constantly, and the confusion causes real inventory mistakes, so it's worth being precise. A UPC (Universal Product Code, part of the wider GTIN family) is a globally unique barcode number issued through GS1 US. It identifies a product to any retailer and supplier — Walmart, Amazon and a mom-and-pop store all read the same UPC as the same item. You can't 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 UPC 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's yours to define, layered on top of their own listing ID and any UPC/EAN 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 an expiration 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 US apparel retailer: category "Hoodie" → HOO, brand "Nova" → NOV, size "Medium" → M, color "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 stores that's category, brand or supplier, size, and color — 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 color 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 isn't more informative than a 14-character one — it's 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's still worth avoiding a leading zero in the design itself.
• Don't encode information that changes — a supplier's cost price, a warehouse bin 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 catalog. 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 periods. Spaces, slashes, ampersands and special characters cause silent failures in CSV imports on Shopify, WooCommerce and most marketplace bulk tools.

Marketplace-specific SKU rules for US sellers

Amazon Seller Central: 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.

Walmart Marketplace: requires a unique SKU per item and, separately, a GTIN/UPC for the product itself — the two are complementary fields in every bulk upload template, and Walmart's item spec rejects listings where the SKU field is left blank or duplicated across active items.

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

Etsy: the "SKU" field on each listing/variation is optional but strongly recommended once you sell more than a handful of products — without it, reconciling orders against your own stock system becomes a manual, error-prone process.

Whichever platform you sell on, GS1 US remains the authority for the UPC/barcode side of your product data — the SKU and the UPC 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/color combinations one at a time. If you stock 4 sizes and 5 colors 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 color names once against Color 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.