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The Ecommerce KPI Glossary
The numbers that matter, in plain English, with the formula and what good looks like. Bookmark it for your next agency report.
| Metric | Formula | Why it matters |
|---|---|---|
| Break-even CPA | AOV + shipping charged - product cost - postage - fees | The most you can pay for an order without losing money |
| Break-even ROAS | AOV / break-even CPA | The platform ROAS below which first orders lose money |
| MER (blended ROAS) | Total sales / total ad spend | The honest view across all channels; ignores attribution arguments |
| CPA | Ad spend / purchases | Cost to win an order on a platform |
| nCAC | Ad spend / new customers | What a genuinely new customer costs |
| AOV | Revenue / orders | Higher AOV raises the CPA you can afford |
| Conversion rate | Orders / sessions | How well the site turns visits into sales |
| Cart to checkout | Checkouts started / adds to cart | The most common hidden leak; often a site issue, not an ad issue |
| Contribution margin | Revenue - variable costs - ad spend | What's left to pay for the business |
| LTV | AOV x orders per year x lifespan x margin | Sets how much you can invest in acquisition |
| CPM | Spend / impressions x 1,000 | The cost of attention; rises in Q4 |
| CTR (link) | Link clicks / impressions | Whether the hook stops the scroll |
| Frequency | Impressions / reach | Above 3 on cold audiences usually signals fatigue |
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