How ROAS is calculated
ROAS is the simplest efficiency ratio in advertising: revenue divided by ad spend. A campaign that produced £80,000 of attributed revenue from £20,000 of spend has a ROAS of 4.0 - four pounds back for every pound in. It is usually quoted as a multiple (4.0x) or, less commonly, as a percentage (400%), and it can be calculated at any level of granularity, from a single ad to an entire account.
The catch hides in the word attributed. ROAS is only as honest as the attribution model that credits revenue back to advertising. A last-click model will hand most of the revenue to bottom-funnel channels and flatter their ROAS, while starving upper-funnel channels of the credit they earned. Two teams measuring the same campaign with different attribution rules can report wildly different numbers, which is why ROAS is best read as a directional efficiency signal rather than an exact truth.
Average ROAS versus marginal ROAS
The ROAS most teams quote is an average: total revenue divided by total spend, blended across every pound and looking backward. It is genuinely useful for reporting, but it is the wrong number for a budget decision. Budgets are decided at the margin - the only question that matters when you add or cut spend is how much new revenue the next pound will create. That is marginal ROAS, and it routinely disagrees with the average.
The two diverge because paid media follows diminishing returns: as spend rises and the most responsive audiences are exhausted, each additional pound returns less. A channel can show a comfortable blended 5.0 average while its last tranche of spend is returning a marginal 1.5 - the average is propped up by all the efficient early spend even after the next pound has stopped paying its way. For the full treatment of when to trust each, see marginal ROAS versus average ROAS.
ROAS vs POAS, and the break-even line
ROAS measures revenue, not profit - and revenue is not money you keep. Cost of goods, discounts, returns and shipping all sit between a sale and its contribution to the bottom line, so a strong ROAS can still be loss-making once margins are accounted for. That gap is exactly what POAS - profit on ad spend - is designed to close, by measuring gross profit per pound of spend rather than top-line revenue. For any business with variable margins across its catalogue, POAS is the more honest test of whether advertising actually makes money.
The number that turns a raw ROAS into a verdict is your break-even ROAS: the point at which gross profit on the revenue exactly covers the spend. If your gross margin is 40%, you break even at a ROAS of 2.5, so a 3.0 ROAS is profitable and a 2.0 is quietly burning cash. This is why there is no universal good ROAS - the only meaningful benchmark is your own margin, not an industry figure pulled from a benchmark report.
The limits of average ROAS for budget decisions
Average ROAS is a reporting metric wearing a planning metric’s clothes. Because it blends every pound into one backward-looking ratio, it hides how efficiency changes with scale and, worse, it credits advertising with revenue that would have arrived anyway. The cleaner question - how much revenue advertising genuinely caused - is captured by iROAS, which strips out baseline demand. A channel that mostly harvests existing intent will post a flattering average ROAS while contributing little incremental growth.
The practical consequence is over-investment in saturated channels. Planning on the average keeps feeding a channel whose blended ratio still looks healthy, long after its next pound has stopped working. The fix is to forecast the response curve and allocate against the margin - which is what ElenIQ does before any spend is committed. You can pressure-test the next-pound efficiency directly with the marginal ROAS calculator, or model a full reallocation in the ad spend forecasting tool.
Related terms
- marginal ROAS - the return on the next pound of spend, which should drive budget decisions instead of the average.
- POAS - profit on ad spend, which accounts for margin where ROAS counts only revenue.
- break-even ROAS - the ROAS at which gross profit exactly covers the spend, set by your margin.
- iROAS - the incremental revenue advertising actually creates, net of baseline demand.
Frequently asked questions
What is ROAS?
ROAS, or return on ad spend, is the revenue an advertising channel or campaign generates for every pound spent on it. A ROAS of 4.0 means £4 of revenue came back for every £1 of spend. It is the most widely used efficiency metric in paid media, but it is a blended average across all spend, so it describes what happened rather than what the next pound will do.
How is ROAS calculated?
ROAS is calculated as revenue divided by ad spend. If a campaign produced £80,000 of attributed revenue from £20,000 of spend, its ROAS is 4.0 (80,000 / 20,000). It is usually expressed as a ratio or multiple rather than a percentage. The figure depends entirely on the attribution model used to credit revenue to advertising, so two teams can report very different ROAS for the same campaign.
What is a good ROAS?
There is no universal good ROAS - the only meaningful benchmark is your break-even ROAS, the point at which gross profit on the revenue exactly covers the ad spend. A 3.0 ROAS is excellent for a high-margin software product but loss-making for a low-margin retailer. Always compare ROAS against your own margins and break-even point, not an industry average.
What is the difference between ROAS and POAS?
ROAS measures revenue per pound of spend, while POAS (profit on ad spend) measures gross profit per pound of spend. ROAS can look strong while POAS is weak, because revenue ignores cost of goods, discounts, returns and shipping. For businesses with variable margins across products, POAS is the more honest measure of whether advertising actually makes money.
Why does average ROAS mislead budget decisions?
Average ROAS blends every pound of spend into one backward-looking ratio, so it hides how efficiency changes as budget grows. Because response curves flatten, a channel can post a healthy average ROAS while the next pound returns almost nothing. Budget decisions are made at the margin, so allocating on average ROAS over-invests in channels that are already near saturation.