The metric behind the media plan
Share of voice (SOV) is the percentage of total category advertising or visibility your brand captures in a set period. Spend $2 million in a category where total ad spend is $20 million and your SOV is 10%.
The metric exists because absolute numbers hide the competitive picture. Your impressions and clicks can rise while a rival triples budget. By the time that shows in sales, you’ve lost ground.
Planners rarely read SOV alone. They compare it with share of market (SOM), your slice of category sales. The gap is excess share of voice, or ESOV. Nielsen’s 2009 study of 123 brands across 30 categories found that 10 points of ESOV added about 0.5 percentage points of market share over a year.
From grocery shelves to Google Ads
The framework started with packaged goods. James O. Peckham analysed Nielsen store-audit data from 1960 to 1978 and concluded new brands should set ad share around one and a half times their target market share after two years. John Philip Jones later split “investing” brands, which spend above market share, from “profit-taking” brands, which spend below it.
Digital made the metric easier to track and easier to game. Google Ads has reported impression share since October 2012, but impression share measures presence against potential, not against rivals. True SOV asks a different question: how much of the conversation do you own?
One term, two very different deals
On the sell side, SOV is inventory allocation—the percentage of ad requests promised to one buyer in advance. Google Ad Manager sponsorships, Amazon reserve placements and Lufthansa seatback pre-roll tiers all sell percentages rather than outcomes.
That creates a planning trap. A reserved 20% share of voice is not a guaranteed 20% of impressions or sales. Amazon’s reserve product promises top-of-search placement “most of the time,” not 100% impression share.
- Always pair SOV with SOM to see whether you’re overinvesting or underinvesting.
- Define the denominator clearly. A narrow competitive set flatters weak brands.
- Treat AI SOV as a range. The IAB prefers “22%, plus or minus four points” over bare figures.
Why AI share of voice is still a beta metric
AI visibility vendors now call brand mentions in chatbot answers “share of voice.” But the data is non-deterministic. Search consultant Lily Ray documented ChatGPT personalisation rewriting prompts per user, so trackers rarely see what customers see.
Standards are catching up. The IAB’s August 2026 guidance made the competitive set and mention-pool size mandatory disclosures, but no independently audited share-of-voice standard yet exists for ChatGPT advertising.
The takeaway for growth teams
Use SOV as a budget question, not a scoreboard. If the ESOV relationship holds in your category, a target market share gain can be turned into an estimated spending requirement—and a budget cut can show the erosion before it arrives.
Just know what you’re buying. On the buy side, SOV is a planning ratio built on estimates. On the sell side, it’s a rate-card promise with caveats. The denominator decides the result.
Source: PPC Land
