What is a SKU, and why do your emails care about it?
Your own code for one exact thing you sell: this product, this size, this colour. Dull to set up, expensive to get wrong, and quietly holding up several of your flows.
- 122SKU (Stock Keeping Unit)
- A unique identifier for each distinct product and service that can be purchased, used to track inventory and sales.
- One per
- Variant: every size, colour or pack that can sell out on its own
- Not the same as
- A barcode number (GTIN), which identifies the product in every shop that sells it
- Set in
- Your ecommerce platform, on each variant
- Read by
- Your stock counts, your warehouse, marketplaces and the order data Klaviyo receives
One product page, many SKUs
A T-shirt in four sizes and three colours is one product page and twelve SKUs, because each of those twelve can sell out on its own. A gift set gets its own SKU too, even when everything inside it already has one.
The SKU is yours, and you can make it anything. That's exactly how shops end up with codes nobody can read. A readable format does a lot of quiet work.
- Short and consistent: range, product, colour, size, in the same order every time
- Letters, numbers and hyphens only, no spaces
- Nothing that changes, like the price or the supplier
- Never reused, even for a product you dropped years ago
SKU, barcode or product ID: who makes which
| Identifier | Who creates it | What it's for |
|---|---|---|
| SKU | You | Stock, picking, and your own reporting |
| Barcode number (GTIN) | You, through a GS1 licence | Retailers, marketplaces and Google Shopping listings |
| Product and variant ID | Your ecommerce platform | Integrations such as Klaviyo, behind the scenes |
| ASIN | Amazon | Listings on Amazon, and nowhere else |
Klaviyo sees two of these. On Shopify, every ordered product arrives with its SKU and its variant ID, so you can build a segment of everyone who bought the large refill without guessing at product names.
Where messy SKUs break your flows without telling you
A replenishment flow filtered on what someone bought stops working when that product comes back under new codes. New buyers never enter it. Old buyers get reminded about something you've stopped selling.
Back in stock alerts work on the exact variant someone asked about, so the back in stock flow is only as good as the stock count behind each SKU. And a relaunch with fresh SKUs splits the order history in two, so a segment built on the new SKU misses everyone who bought the old one.
Related terms
FAQs
What's the difference between a SKU and a barcode?
A SKU is your own code, in whatever format you choose, for stock and orders. A barcode carries a GTIN, a number issued through GS1 that means the same product in every shop that sells it. Retailers, marketplaces and Google Shopping ask for the GTIN. Your warehouse runs on SKUs.
Should SKUs mean something or just be numbers?
Mean something, within reason. A SKU your team can read at a glance saves picking mistakes and makes reports easier to scan. Keep it short, keep the parts in the same order everywhere, and leave out anything that changes, like price or supplier.
Can two listings share one SKU?
Yes, if they're the same physical thing. That's the point: an item sold on your site and on a marketplace should share a SKU so the stock count stays honest. Two different things should never share one, however alike they look, because one of them will sell out first.
Rather we explained it on your own account?
Bring your Klaviyo account to a growth consultation. We'll walk through what this means for your numbers, in plain English, and what we'd fix first.
Half an hour with Theo, our founder.
We're all about relationships built on trust, mutual respect and a shared vision for success. If that sounds like your vibe, let's make some waves together 🌊
