The dozen numbers worth checking weekly, from conversion rate and contribution margin to TACoS, stock cover and account health, and how to read them together.
Most sellers need about a dozen numbers each week: sales, sessions, conversion rate, average order value, contribution margin, advertising efficiency (ACoS, ROAS and TACoS), days of stock cover, stock-outs, returns rate, customer service response and marketplace account health. Track them for each channel, on the same day each week and with fixed definitions, then read them together rather than one at a time. A single number tells you what happened; the combination usually tells you why.
Sales and traffic
Start with the top line, and agree how it is counted. UK sellers should usually report sales excluding VAT and net of refunds, otherwise growth can look better than it is.
- Sales: net revenue, orders and units for the week.
- Sessions: visits to your store or listings. On marketplaces, use the platform's own count.
- Conversion rate: orders divided by sessions. Amazon's Business Reports use units divided by sessions, called Unit Session Percentage, so do not compare it directly with your Shopify figure.
- Average order value (AOV): revenue divided by orders.
These are linked: sales equal sessions multiplied by conversion rate multiplied by AOV. When sales move, at least one of those three inputs has moved, and that is where to look first.
Profit and advertising
Revenue growth means little if each sale loses money. Contribution margin is what remains from each sale after the costs that rise with every unit: the product's landed cost in the UK (including freight and duty), marketplace and payment fees, fulfilment and packaging, an allowance for returns and the advertising spent to win the sale. Express it as a percentage of net revenue and as profit per unit for your main products. Fixed overheads such as rent and salaries sit outside this figure.
For advertising, three ratios cover most needs:
- ACoS: ad spend divided by the sales attributed to ads, as a percentage. Amazon Ads points out that to stay profitable, ACoS must be lower than your profit margin before advertising.
- ROAS: attributed ad sales divided by ad spend, the inverse of ACoS and the usual measure on Google and Meta.
- TACoS: ad spend divided by total sales, organic included. It is an industry term rather than a standard platform report, so calculate it yourself. It shows how dependent your sales are on paid traffic.
Each platform attributes sales using its own rules, so not every attributed sale is an extra sale. Watching TACoS and contribution margin alongside ACoS or ROAS keeps that in check.
Inventory
Stock problems damage marketplace rankings and tie up cash, so check them weekly:
- Days of cover: units available divided by average daily units sold over recent weeks. Compare it with your reorder lead time plus a safety buffer.
- Sell-through rate: units sold in a period as a share of the units available to sell in that period. Definitions vary, so choose one and keep it.
- Stock-outs: how many SKUs are out of stock, for how many days, and an estimate of the sales lost.
- Ageing stock: units that have not sold within a set period and may be attracting storage fees.
Returns, customer service and account health
Returns rate is units returned divided by units sold, ideally broken down by product and reason. Returns arrive weeks after the sale, so compare them with sales from the period they relate to. Customer service needs only a few measures: messages received, the share answered within the marketplace's expected time and the main reasons customers get in touch.
Marketplaces publish their own health measures, and they matter because falling short can restrict or suspend your selling:
- Amazon's Account Health page covers customer service performance, policy compliance and shipping performance, including Order Defect Rate, which Amazon asks sellers to keep below 1%, along with late dispatch, cancellation and valid tracking rates.
- eBay's seller standards measure transaction defect rate, late delivery rate and cases closed without seller resolution, with seller levels evaluated on the 20th of each month.
- Etsy looks at average review rating, message response rate and case rate over the past three months, and these also feed into its search ranking.
Building a simple weekly scorecard
A spreadsheet is enough. Keep it to one page so that it actually gets read.
- One row per metric, grouped as above, and one column per week so trends are visible at a glance.
- A separate block for each channel, plus a combined total.
- For each metric: this week, last week, the four-week average and the target, with a simple red, amber or green flag.
- A written definition and data source for every metric, so the numbers mean the same thing every week.
- A notes row for events such as price changes, promotions, stock-outs, listing edits and new campaigns.
- A named owner for each metric who explains any red flag.
Pull the figures on the same day each week for the same Monday-to-Sunday period, and drop any metric nobody acts on.
Reading the numbers together
Patterns are more useful than any single figure. Some common ones:
- Sales down, sessions down, conversion steady: a traffic problem. Check rankings, ad budgets, suppressed listings and seasonality.
- Sessions steady, conversion down: something on the listing or offer has changed. Check price, stock, reviews, delivery promise, competitors and, on Amazon, whether you hold the Featured Offer (Buy Box).
- Sales up, contribution margin down: growth is being bought with discounts or advertising. Check TACoS and fees.
- ACoS steady but TACoS rising: organic sales are shrinking, so ads are carrying more of the load.
- Conversion up, then returns up a few weeks later: the listing may be over-promising.
- Days of cover falling below lead time: reorder now, before a stock-out costs you ranking.
Use the four-week average to judge direction, and be wary of conclusions drawn from small numbers: a product selling ten units a week can swing widely by chance.
How Farioxa can help
Farioxa's analytics service builds weekly scorecards for marketplace and web store sellers, bringing sales, advertising, inventory and account health data into one consistent report with agreed definitions. Our account management team can also review the numbers with you each week and turn them into a list of actions.
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