Ecommerce inventory management: make the number online match the shelf

Ecommerce inventory management is the work of keeping one number honest: the figure a customer sees next to "in stock" when they are deciding whether to buy from you. Everything else in this guide exists to serve that one number.

This page is for the person who runs a webshop and holds the goods themselves. You store the stock, you pick the orders, and the figure on the product page comes out of a system you control. It is written for operations from one person with a few hundred order lines a week up to a team of a dozen. It is not written for sellers whose stock sits entirely with a fulfilment partner, and not for operations already running a warehouse system; the way of looking at the problem still holds, but the fixes will not.

First: do you need anything for this?

If you sell on one channel, hold a few hundred lines, and the person who picks the orders is the same person who put the goods away, your webshop platform's own stock counter plus a regular count will carry you a long way. Many perfectly good businesses run on exactly that. The honest test is not how big you are. It is whether you can answer this question without walking into the warehouse: for your best-selling line, what can you sell right now? If the answer comes back in seconds and turns out to be right, you do not have a problem to solve.

Read on when the answer takes a walk, an argument, or a phone call.

Why the number online stops matching the shelf

Stock figures do not drift for mysterious reasons. They drift for five, and they are all mundane.

Goods move without being recorded. Someone takes a unit for a photograph, a sample or a replacement and the system never hears about it. The wrong item is picked. The customer is happy, the figure for two separate lines is now wrong, and nobody finds out until one of them runs dry. A return comes back and sits in a corner: the customer has been refunded, so the money has moved, but the unit is neither back on sale nor written off. Something is damaged or lost and is quietly worked around rather than booked out. And finally, a second channel sells the same unit you just sold, because the two were never looking at the same figure at the same moment.

Notice that only the last of these is a software problem. The other four are habits.

Three figures, not one

Most of the damage comes from treating stock as a single number. It is three.

Physical stock is what is on the shelf. You can walk up and touch it.

Committed stock is the part of that physical stock already promised to orders you have accepted but not yet despatched. It is still in the building. It is not yours to sell.

Available to sell is physical minus committed, minus anything damaged or awaiting inspection. This is the only figure that should ever reach a product page or a marketplace listing.

When those three collapse into one, you get the two classic failures at once. You oversell, because the channel was reading physical stock. And you refuse orders you could have filled, because somebody padded the figure downwards by hand to stop the overselling.

Five habits that keep ecommerce inventory management honest

None of these require software. All of them are harder without it.

Give every item one fixed location. Not a shelf it usually lives on. One location, written down, the same one every time. Most counting disputes are really search problems.

Book the movement when it happens, not at the end of the day. A movement recorded three hours later is a figure that was wrong for three hours, and the orders accepted in those three hours were accepted against a lie.

Scan rather than read. A barcode scan at the point of pick removes the single most common error in the whole operation, which is a person reading one line of a list and picking from another. Our barcode generator will produce labels if your supplier does not.

Count a little, often. Pick your fastest-moving lines and count them weekly. Put the rest on a fixed rotation. This is called cycle counting, and it beats an annual stocktake for one reason: it finds the error while the error is still small. The cycle count calculator will tell you how many lines a day that means for your range.

Measure how wrong you are. Count a sample, compare it with the system, and record the percentage that matched. One number, tracked weekly. Without it, every discussion about stock accuracy is a matter of opinion.

Selling on more than one channel

This is where a webshop operation usually stops coping, and the wider subject of multichannel inventory management is covered on its own page. One Shopify store with a thousand lines is a bookkeeping exercise. The same thousand lines listed on Amazon, eBay and your own store is a timing problem, and timing problems cannot be solved by being careful.

The mechanics are simple enough to state. Every channel holds its own copy of your stock figure. Each copy is refreshed on a schedule, or when a sale triggers an update, and between refreshes it is out of date. Sell the last unit on eBay and Amazon continues offering it until the next sync lands. That gap is where overselling lives, and on a marketplace an oversell is not merely an apology: it is a cancellation against your seller metrics.

There are three defences, and most operations end up using all three. Hold one master stock figure and push it out, rather than maintaining a figure per channel. Shorten the interval between updates. And keep a small buffer on your fastest lines, so that the last unit is never the one being raced over — the safety stock calculator sizes that buffer from your own demand variation rather than from a guess.

On Shopify inventory management specifically, it is worth being clear about what the platform does and does not do. Shopify tracks stock per location and decrements it on sale, which is genuinely useful. It does not know that a pick went wrong, that a unit is damaged, or that a return is sitting unopened on a bench, because none of those events happen inside Shopify. The same holds for WooCommerce. The platform is an accurate record of what it was told, which is not the same thing as an accurate record of your warehouse. Where several channels are in play, a marketplace hub such as ChannelEngine or a connected warehouse system becomes the thing holding the master figure, and the channels become consumers of it.

If you sell food, cosmetics or supplements

Stock with an expiry date is not one figure per product. It is one figure per batch, because two units of the same product with different expiry dates are not interchangeable. You need the batch number recorded at goods-in and carried through to the despatch note, so that a recall is a query rather than an archaeology project, and so that the oldest stock goes out first. Spreadsheets handle this badly. It is one of the clearest cases where software stops being a convenience.

When you outgrow a spreadsheet

A spreadsheet fails at a predictable point: when two people need to change it at the same time, or when the figure has to be true at the moment of sale rather than at the end of the day. Before that point, a spreadsheet and a disciplined routine beat software that nobody updates. After it, no amount of discipline helps, because the problem is no longer carelessness but simultaneity.

The signals are concrete. More than one person picks from the same shelf. You sell on more than one channel. Stock carries batch or expiry dates. You hold stock in more than one place. Or you have started padding your online figures downwards to stop overselling, which means you are already paying for the problem in refused orders.

If you have reached that point, our pages on inventory management software and what an inventory management system actually holds cover the selection question, which is a different question from this one.

Frequently asked questions

What is ecommerce inventory management?

It is the work of keeping three figures straight: what is physically on the shelf, what is already committed to orders you have accepted, and what is therefore still available to sell. The third figure is the only one a sales channel should ever be shown.

Why does my webshop sell items I do not have?

Almost always because the channel is reading a figure that has not been reduced for stock already committed, damaged or returned but not yet inspected. The stock was never there to sell; the number simply had not caught up.

How often should I count stock?

Count a small number of lines often rather than everything once a year. Weekly for your fastest movers, a fixed rotation for the rest. A full annual count that closes the operation tells you the size of the problem long after it cost you the money.

Do I need inventory software for my webshop?

Not if you sell on one channel, hold a few hundred lines, and the person who picks also knows where everything is. Software earns its place when you sell on more than one channel, when stock carries batch or expiry dates, or when more than one person picks from the same shelf.

Continue with

• Picking and shipping for webshops — what happens after the order is accepted
• Returns — getting the unit back on sale or written off
• Peak season — what breaks first when volume triples
• E-commerce — the wider picture for online retail

Two questions about your own operation

For your best-selling line, what can you sell right now, and when did you last check that figure against the shelf?

If a customer asked today which batch their order came from, how long would the answer take?