Metrics & KPIs

ACoS vs AOV: Ad Efficiency vs Basket Size

In short: These measure different parts of the same sale. ACoS tells you what share of that sale's revenue went to advertising; AOV tells you how big the sale was in the first place. A campaign can hold a flat ACoS while AOV climbs, meaning the same efficiency ratio is now generating more revenue per order. Watch them together, because a falling ACoS paired with a falling AOV usually means smaller, cheaper orders are winning, not genuine efficiency gains. Use ACoS to judge spend efficiency, use AOV to judge whether the orders behind that efficiency are actually growing in size.

By the AdFlint research team · Fact-checked against current Google and Meta platform behavior · Last reviewed July 2026

ACoS

Advertising spend divided by attributed sales revenue, expressed as a percentage; the inverse of ROAS, and the standard vocabulary on Amazon.

Lower is better here, the opposite direction from ROAS, which is where most confusion starts when teams report both. Twenty-five percent equals a four-times ROAS. It also says nothing about profitability until you set it against your break-even margin. The usual misreading is reading a falling number as growth, when it often accompanies shrinking volume instead.

Full definition

AOV

Total revenue divided by the number of orders in a period, the average amount a customer spends per transaction.

It is the lever connecting conversion rate to ROAS: raising it improves returns without winning a single additional customer. Being an average, a handful of large orders can pull it well above what a typical buyer spends. The common misreading is tracking it without the median or product mix behind it, then crediting a promotion-driven swing to a creative change.

Full definition

Side by side.

The differences that actually change what happens in your account.

 ACoSAOV
What it's a ratio ofSpend over attributed sales revenue.Revenue over order count, not a spend ratio at all.
Direction of goodLower is better.Higher is generally better, within reason.
What moves itBids, keyword targeting, conversion rate, and price.Bundling, upsells, minimum-order incentives, and product mix.
Sensitivity to spendDirectly a function of ad spend.Unaffected by ad spend, purely a function of what's in the cart.
What a good number alone provesEfficient spend relative to sales, and nothing about order size.Large orders, and nothing about how much it cost to win them.
Common misreadA falling ACoS is assumed to mean growth, when order volume can be shrinking underneath it.A rising AOV is assumed to mean healthier margin, when it can be driven by discount-bundling that hurts margin.
Where it reportsAmazon Ads console, or spend-to-sales dashboards elsewhere.Ecommerce or storefront analytics, independent of any ad platform.

What actually separates them.

01

ACoS includes ad spend in its formula; AOV does not include ad spend anywhere in its calculation.

02

ACoS is a percentage that improves as spend efficiency improves; AOV is a dollar figure that improves as basket size grows, and neither one moving is caused by the other moving.

03

You can lower ACoS by cutting spend on low-converting keywords without touching AOV at all, since basket size is a checkout-side outcome, not a bidding outcome.

04

AOV can be pushed up with discounts or free-shipping thresholds that simultaneously push ACoS higher, because bigger discounted baskets often convert at a higher cost per sale.

05

ACoS is calculated per campaign or per attribution window; AOV is usually calculated store-wide or per traffic source, so the two are frequently reported at different levels of granularity.

Which one should you use?

Use ACoS when

  • You're deciding whether to raise or lower bids on a specific campaign or keyword.
  • You need a single number to compare spend efficiency across campaigns.
  • You're setting a target for how much of each sale's revenue advertising is allowed to consume.
  • You're troubleshooting why a campaign's profitability changed without a big revenue swing.

Use AOV when

  • You want to know whether merchandising changes, like bundles or cross-sell, are working.
  • You're diagnosing whether a ROAS or ACoS change came from order size rather than ad efficiency.
  • You're forecasting revenue from a fixed number of expected orders.
  • You're comparing basket size across customer segments or acquisition channels.

Common questions.

If ACoS improves but AOV drops, is that good news?

Not necessarily. It often means the campaign is winning more small, cheap orders rather than becoming genuinely more efficient, so check order volume and total revenue before calling it a win.

Can raising AOV lower my ACoS?

It can, since ACoS's denominator is sales revenue and a bigger basket raises that revenue without necessarily raising spend. This is why upsells and bundling at checkout are a legitimate lever for improving ACoS even without touching bids.

Which one should I check first when a campaign's numbers look off?

Check AOV first to rule out a basket-size shift, then look at ACoS to see if efficiency actually changed. Separating the two keeps you from misdiagnosing a merchandising change as a bidding problem or vice versa.

Does a low ACoS mean the campaign is profitable?

Not on its own. ACoS only tells you spend as a share of revenue, not margin, so a low ACoS on low-margin products can still lose money, which is why you need to check it against a break-even ACoS built from actual product margin.

Or stop choosing between them.

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