Share of Voice in Marketing: The Budget Metric That Predicts Market Share

Share of voice (SOV) is your brand's share of the total advertising presence in the category — of everything the category spends to be seen and heard, the proportion that is yours. It is a market-level metric, not a channel metric. It measures how loudly your brand speaks relative to the whole category conversation, not just relative to last month or last year.

The reason it matters is not the number itself. It is the relationship between SOV and something else: your share of market (SOM). Set the two against each other, and you have one of the oldest and most consistently replicated findings in advertising effectiveness research.

The SOV–SOM relationship

Brands whose share of voice runs above their share of market tend to grow. Brands whose share of voice runs below it tend to shrink. This pattern holds across categories, countries, and decades with a level of consistency that is rare in marketing research.

John Philip Jones documented it first, in the Harvard Business Review in 1990, analysing 23 brands across categories in the US. Les Binet and Peter Field quantified it across the IPA effectiveness databank — hundreds of case studies covering multiple decades of advertising effectiveness data. Robert Brittain and Peter Field validated it again on the Advertising Council Australia's effectiveness database.

Different decades. Different markets. Same finding.

The difference between a brand's share of voice and its share of market has a name: excess share of voice (ESOV).

Why challengers need excess SOV more than leaders do

The SOV–SOM equilibrium line is not straight. It is concave — and that shape is commercially important.

A brand with 15% of the market needs well over 15% of the category's voice just to hold its current position. A brand with 40% market share can often hold position at or slightly below 40% SOV. The market leader has a structural voice advantage: they can maintain share at lower relative investment.

This is Double Jeopardy arriving in the media budget. The smaller brand pays twice: fewer buyers, and a structurally higher voice investment required per point of share. For a challenger brand building a growth plan, this is not optional context. A plan that projects market share growth without planning excess share of voice has a target, not a plan.

The implication is uncomfortable: challenger growth requires spending at a higher share of the category's total media investment than your current share of its sales. That means the challenger CMO's budget conversation is always structurally harder than the market leader's. The data doesn't change that. It just means the argument has to be made explicitly rather than optimistically.

How to measure share of voice in 2026

Media fragmentation has made SOV harder to measure cleanly than it was when Jones documented the original SOV–SOM relationship in traditional media. There is no single source that sees all of a category's voice across digital, social, TV, audio, OOH, and press simultaneously. In practice, you triangulate from three or four sources:

Ad spend estimates. Nielsen Ad Intel, WARC, and media agency competitive reports estimate total category advertising spend by brand across traditional channels. The strongest data is in TV-heavy categories; the weakest is in digitally fragmented categories where a significant share of spend runs in formats that are not captured by spend trackers.

Social and earned share of voice. Tools like Brandwatch, Meltwater, or Mention count brand mentions across social media and news against a defined competitor set. This is a presence measure, not a spend measure — it captures the voice that landed in organic conversation, not just the voice that was bought. Directionally useful; not directly comparable to spend-based SOV.

Digital transparency tools. The Meta Ad Library and Google Ads Transparency Center show every ad a competitor is currently running. No spend figures are available, but a fast, free audit of who is in market with what creative gives a read on competitive activity. Useful for directional competitive monitoring at zero cost.

Share of search. Introduced as an SOV proxy by Les Binet, share of search measures what proportion of branded search queries in the category include your brand name. It captures the voice that landed — the awareness that became active enough to produce a search — rather than the voice that was bought. It is free to track via Google Search Console and Google Trends. And it leads market share changes by approximately six months, making it a leading indicator rather than a lagging measure.

For most businesses, the practical measurement system combines one or two of these with a clear definition of the competitor set and a consistent monthly tracking cadence. Precision is less important than consistency — the trend over twelve to twenty-four months is the signal; any single month's reading is noise.

Share of search: the free leading indicator

For the CMO who cannot afford media spend tracking or quarterly brand awareness surveys, share of search is the single most important SOV proxy available.

To calculate it: identify the set of branded search terms that represent your category — typically your brand name plus the category keyword, set against two to five competitors. Use Google Trends to track relative search interest over time. Your brand's share of total branded search volume in the category, tracked monthly, is a working proxy for mental availability and effective share of voice.

What makes it particularly useful as an argument tool: it leads financial outcomes. Binet's research across multiple categories found that changes in share of search precede changes in market share by approximately six months. A brand whose share of search has been rising for three months is building mental availability that will translate into share before the financial data confirms it. A brand whose share of search is declining is losing mental availability — and the revenue implication will arrive before it appears on the P&L.

For the CMO defending brand investment in Phase 1 of a long-term programme, this is the early-warning signal that makes the argument possible without a tracking study: "Share of search is up 4 points since we started the campaign. Based on the six-month lag, we expect that to show up in market share data in Q2."

Making the SOV argument to the CFO

The power of the SOV framework is that it converts the budget conversation from taste to arithmetic. "We need more brand budget" is an opinion. "Our current share of voice is 9%, our share of market is 14%, and negative ESOV predicts share decline within twelve months" is a forecast the CFO can evaluate and test.

The argument structure:

1. State the category's estimated total advertising weight (total spend or search volume baseline)
2. State your current SOV and your current SOM
3. Calculate your current ESOV (positive = growth territory, negative = decline territory)
4. State the SOV target required to achieve the growth plan's market share objective
5. State the budget implication — the incremental investment needed to move from current SOV to target SOV
6. Reference the Binet & Field rule of thumb: ten ESOV points → roughly half a point of SOM per year

This is not a guarantee. The Binet & Field rule of thumb is an average across many categories, and your specific category will deviate from the average in ways that matter. But it is a specific, evidence-grounded prediction that gives the CFO something to evaluate — which is categorically more useful than a request for more brand budget justified by brand importance.

The recession opportunity

One property of ESOV matters most precisely when budgets are under pressure: it gets cheaper in a downturn. When competitors cut their media spend, the category's total voice shrinks. The same absolute budget that delivers +2 ESOV in an expansionary market can deliver +8 in a market where three competitors have cut simultaneously. At recession media prices, the share of voice per euro of spend improves materially.

This is the documented reason why brands that maintain or increase investment during downturns consistently emerge stronger than those that cut. They are not buying more impact per se — they are buying a larger share of a smaller pool, at a lower cost per unit of share, at the exact moment when the weaker brands are reducing theirs. The competitive advantage compounds in the quarters after the downturn ends, precisely because the mental availability built during the contraction is still working.

The CMO who can make this argument before the downturn — with the ESOV framing ready, the competitor spend tracker in place, and the share of search trend as supporting evidence — is in a very different position in that budget meeting than the one who cannot.