Free tool
Free SKU generator
Enter a product and its colors, sizes or scents. You get a consistent SKU for every variant, duplicates flagged, and a CSV with a UPC column ready to fill.
How to use the SKU generator
A SKU (stock keeping unit) is a code you create to track one exact product variant in your own inventory, such as ACM-TS-BLK-M for a black, medium Acme T-shirt. This free SKU generator builds one for every color and size combination, flags duplicates and exports a CSV. It runs in your browser, and nothing is sent or stored.
- Type your brand or a short prefix (optional), then the product name. Acme and T-Shirt become ACM and TS.
- Add up to 3 attributes. Give each a name, like Color or Size, and type its values separated by commas: Black, Navy Blue, Grey.
- Pick a separator (hyphen, underscore or none) and a segment length of 2, 3 or 4 characters.
- Want a running number on the end? Set a start number. It’s zero-padded to 3 digits, so 1 becomes 001.
- Check the list for flags, then use Copy SKUs or Download CSV. The CSV has columns for SKU, Product, each attribute and an empty UPC column.
Brand Acme, product T-Shirt, Color “Black, Navy Blue” and Size “S, M, L” gives six SKUs, from ACM-TS-BLK-S to ACM-TS-NB-L. The tool makes every combination, up to 2,000 per run, and tells you how many UPC codes those variants need.
How the tool shortens names
Each segment is shortened by three rules:
- Values that already fit stay as typed: S, XL, Red.
- Values with several words become initials: Navy Blue becomes NB.
- Longer single words keep the first letter plus the consonants: Black becomes BLK, Grey becomes GRY, Medium becomes MDM.
Don’t like a code? Type your own after an equals sign. Grey=GY gives GY. 12 oz=12OZ fixes the 12O that the shortening rule would otherwise produce.
What makes a good SKU
A good SKU tells your team what the item is at a glance and never points at two different products. The rules:
- One SKU per variant. Shopify says SKUs in your admin must be unique, and eBay requires a separate SKU for each variation in a multi-variation listing.
- Same order every time. Brand, product, then attributes, from general to specific.
- Start with a letter. All-number SKUs lose leading zeros in spreadsheets.
- Letters, numbers and one separator. Shopify warns against spaces, special characters and formats where 0 and 1 can be confused with O and I.
- Short. Shopify suggests no more than 16 characters.
- Nothing that changes. Leave price, supplier and season out.
Every SKU below is real output from the tool:
| Product and variant | Settings | SKU |
|---|---|---|
| Acme T-shirt, Black, M | Hyphen, 3 characters | ACM-TS-BLK-M |
| Acme T-shirt, Navy Blue, L | Hyphen, 3 characters | ACM-TS-NB-L |
| Acme T-shirt, Black, S, numbered from 1 | Hyphen, 3 characters, start 1 | ACM-TS-BLK-S-001 |
| Candle, Lavender, 8 oz (no brand) | Hyphen, 3 characters | CNL-LVR-8OZ |
Candle, Vanilla, 12 oz with 12 oz=12OZ |
Hyphen, 3 characters | CNL-VNL-12OZ |
| Acme hoodie, Grey, Small | Underscore, 3 characters | ACM_HD_GRY_SML |
| Mug, Red, numbered from 7 | No separator, 3 characters, start 7 | MUGRED007 |
Common SKU mistakes
Sellers send us spreadsheets of their variants when they match barcodes to products, and the same problems come up again and again.
- One SKU for every size. Stock for all sizes merges into one number, so you can’t see that the medium sold out. You also can’t attach a separate UPC to each size, which Amazon and Walmart expect.
- Two values shrinking to one code. At the 2-character setting, Black and Brick both become BK, so a mug in both colors gets MG-BK twice. The tool flags duplicates in the list. Fix it with
Brick=BRKor switch to 3 characters. - Platform-made SKUs. When you add variants, “Shopify automatically generates new SKUs for the additional variants by appending a number to the original SKU”. A trailing number says nothing about color or size.
- All-number SKUs. Excel and Google Sheets turn them into numbers when you open a CSV, so 00125 becomes 125, and Square users report the zeros can’t be recovered from the damaged file.
SKU vs UPC vs ASIN vs FNSKU
A SKU is yours and means nothing outside your business. Amazon’s own guide puts it this way: the same product at a different company can have different SKUs, while its GTIN stays the same wherever it’s sold.
| Code | Who creates it | Format | What it identifies | Where it’s used |
|---|---|---|---|---|
| SKU | You | Any letters and numbers you choose | One variant in your stock | Your inventory, listings, warehouse |
| UPC (GTIN-12) | Brand owner, from a GS1 number | 12 digits, the last a check digit | One product variant, worldwide | Amazon, Walmart, Google, retail tills |
| ASIN | Amazon | 10 letters and numbers | A product in Amazon’s catalog | Amazon only |
| FNSKU | Amazon | Amazon barcode sticker | Your units in Amazon’s warehouses | Amazon FBA |
Every variant that gets a SKU also needs its own UPC if you sell on Amazon, Walmart or into retail. GS1 says each product variation needs its own GTIN: every size, every color and every combination. Walmart requires a unique product ID for each item and says SKU numbers aren’t valid product IDs.
That’s why the tool shows “N variants = N UPC codes needed”. The six Acme T-shirts need six codes, and our 10-pack is $15 one-time with no renewal (current prices: buy UPC codes). Our guide to how many UPC codes you need covers bundles and multipacks.
One honest caveat. Our codes aren’t registered to your company in GS1’s database, and Amazon checks product IDs against GS1 data. Walmart’s onboarding asks for GS1 company prefix codes, and many retail chains want GS1 codes in your own name, so for those, going direct to GS1 is the better choice. Read UPC codes for Amazon before you buy for Amazon.
On Amazon you may also need the FNSKU. For inventory shipped on or after March 31, 2026, resellers without the Brand Representative role must use Amazon barcode stickers even when the product has a manufacturer barcode.
Once your UPCs arrive, paste them into the CSV’s empty UPC column, then make scannable images with the barcode generator or print sheets with the barcode label generator.
How long can a SKU be?
Shorter than any channel will reject. Here’s what the platforms publish:
| Platform | What the platform says | Source |
|---|---|---|
| eBay | 50 characters maximum. Custom Label in seller tools is the same field | eBay Trading API, eBay KB |
| Shopify | No hard cap published. Recommends no more than 16 characters | Shopify Help |
The tool flags any SKU over 40 characters, a safe ceiling when one SKU has to work on several channels. You’ll rarely get near it: four 3-letter segments with hyphens come to 15.
When to change a SKU, and when never to
Change a SKU only when the old one is wrong or clashes with another, and do it on purpose, one channel at a time.
On Amazon, a new SKU doesn’t need a new ASIN. An Amazon staff member on Seller Forums confirmed you can send in your items with a new SKU on the same ASIN. If your units carry FNSKU stickers, though, run down the stock on the old SKU first, because those stickers are tied to it.
Walmart has a SKU Update column in its item setup template. The item keeps its ratings and reviews, but Walmart warns that incorrect entries may result in data loss, so use it only when you mean to replace a SKU.
Never give a retired SKU to a different product. Old orders, returns and reports still point at it. Barcodes have their own rules; see whether you can reuse UPC codes.
Frequently asked questions
What is a SKU generator?
A SKU generator is a tool that builds stock keeping unit codes from your product details. You type a product name and its attributes, such as color and size, and it shortens each one into a code and joins them in a fixed order. Ours makes a SKU for every variant combination at once, up to 2,000.
Do I need a separate SKU for every size and color?
Yes. Each variant you stock and sell needs its own SKU, or your inventory counts merge. Shopify says no two variants should share a SKU, and eBay requires unique SKUs within a variation listing. If you sell on Amazon or Walmart, each of those variants also needs its own UPC.
Is a SKU the same as a UPC?
No. You invent a SKU to track stock inside your business, and it can be any letters and numbers you like. A UPC is a 12-digit number from the GS1 system that identifies the product to marketplaces, retailers and checkout scanners. Most sellers use both, one of each per variant.
How long should a SKU be?
Aim for 16 characters or fewer. Shopify recommends no more than 16, and eBay’s Custom Label field stops at 50. This tool flags anything over 40 characters as a safe ceiling for selling on several channels. Three or four short segments joined by hyphens usually land between 10 and 16.
Should a SKU start with a letter or a number?
Start with a letter. Spreadsheets treat all-number SKUs as numbers, so a SKU like 00125 loses its leading zeros when someone opens the CSV in Excel or Google Sheets. Starting with a brand or product code avoids that, and it makes the SKU easier to read on a picking list.
Is my product data saved anywhere?
No. The SKU generator runs entirely in your browser. Your brand, product names and attributes aren’t sent to our server or stored, so closing the page clears them. Use Copy SKUs or Download CSV before you leave if you want to keep the list.
Got your SKUs? Now get a UPC for each one.
Every size and color you sell on Amazon or in stores needs its own UPC. Ours cost a one-time price with no renewal fees, and arrive by email, usually within 15 minutes.