Why ROAS is the wrong marketing metric for most SME owners

What ROAS actually measures

ROAS is simple: revenue generated divided by advertising spend. A 4x ROAS means that for every pound spent on advertising, four pounds of revenue was generated. This sounds like a useful measure of marketing effectiveness, and as a starting point it is. But it has a fundamental flaw for any business that is not operating at 100% margin: it ignores the cost of the goods or services being sold.

A 4x ROAS at a 40% gross margin means that each pound of ad spend generates four pounds of revenue, and £1.60 of gross profit. Marketing is paying for itself and generating a surplus. A 4x ROAS at a 20% gross margin means the same spend generates the same revenue but only £0.80 of gross profit. Marketing is destroying value at the gross profit level — every pound spent returns less than a pound in gross profit.

The difference between these two businesses is not visible in ROAS. It is visible only in profit ROAS, which applies the gross margin to the revenue ROAS figure to produce the actual gross profit return per pound of marketing spend.

Calculating profit ROAS

Profit ROAS is calculated by multiplying revenue ROAS by gross margin percentage. A 4x ROAS at 45% gross margin produces a profit ROAS of 1.8x — each pound of marketing spend returns £1.80 in gross profit. A 3x ROAS at 30% gross margin produces a profit ROAS of 0.9x — each pound of spend destroys value at the gross profit level, even though the revenue ROAS looks acceptable.

Break-even ROAS — the minimum revenue ROAS required for marketing to cover its own cost in gross profit terms — is 1 divided by gross margin. At 40% gross margin, break-even ROAS is 2.5x. Any channel consistently below 2.5x is loss-making at the gross profit level and should be paused before any budget increase is considered. At 25% gross margin, break-even ROAS is 4x. A channel returning 3.5x looks reasonable in most reporting dashboards but is actually generating a negative gross profit return.

The most common mistake in marketing budget decisions: setting a ROAS target without reference to gross margin. A 3x ROAS threshold appropriate for a 40% margin business will cause a 25% margin business to invest heavily in loss-making activity.

Channel-level profit ROAS

Most multi-channel marketing setups have significant variation between the best and worst performing channels. In a typical setup, the range from highest to lowest ROAS might be 2x to 6x — a threefold difference in revenue efficiency. When gross margin is applied, the profit ROAS range might be 0.6x to 2.7x. The worst channel is actively destroying gross profit. The best channel is generating a strong commercial return.

The most immediately valuable action available to most businesses with a marketing budget is not to increase total spend — it is to reallocate existing spend from the lowest profit ROAS channels to the highest. In practice, cutting the bottom 20–30% of channel spend and reallocating to the top performers typically improves blended profit ROAS by 30–50% without any increase in total budget.

This reallocation is visible in the data. It is not a judgment call about creative quality or audience relevance. It is an arithmetic decision about gross profit return per pound of spend, made at the channel level rather than the blended level.

Marketing as a percentage of revenue

A second useful metric that most SME owners do not track is marketing spend as a percentage of revenue. For most UK product and service SMEs, a marketing spend of 3–8% of revenue represents an active investment in acquisition. Below 2%, the business is largely relying on referrals and repeat business — which may be fine strategically, but is a choice worth making deliberately. Above 10–12% at sub-40% margins, the burden on gross profit becomes significant.

This percentage provides a second check on whether total budget is appropriate, independent of individual channel performance. A business spending 1.5% of revenue on marketing and wondering why growth is slow may need to increase spend before optimising allocation. A business spending 15% on marketing at a 30% gross margin has a structural problem regardless of what the ROAS figures show.

What to track instead

Three metrics that give a more complete picture of marketing commercial performance. First, profit ROAS by channel — revenue ROAS multiplied by gross margin — updated monthly. Second, break-even ROAS based on current gross margin — the floor below which a channel is loss-making. Third, marketing spend as a percentage of revenue — to ensure the total budget is appropriate relative to business scale.

These three numbers, tracked monthly by channel, give an SME owner more actionable commercial intelligence than any amount of impression and click data. The question is not whether an ad was seen or clicked. The question is whether the pound spent on that ad returned more than a pound in gross profit.