Market share by rooftop
What is market share by rooftop: the location-level share number explained
Market share by rooftop is the share of vehicle registrations in a defined geographic area that one dealership location accounts for, measured site by site rather than for the group or the brand as a whole. It is the number a manufacturer's field team opens a performance review with, and the number a group uses to decide which site gets the next investment.
The same measure travels under several names. Sales effectiveness, market penetration, share of registrations, and share of segment all describe versions of it, and the manufacturer's version rarely matches the one you built yourself.
What does market share by rooftop mean?
A rooftop is a single dealership site. Group-level share averages away the thing you can act on, because a strong site and a weak one twenty miles apart produce a respectable middle number and no instruction about what to do next.
Rooftop share is normally measured inside a Primary Market Area, the geography the manufacturer allocates to that site, sometimes called the area of responsibility. PMAs are drawn from census tracts or postcodes, not from where your customers happen to live, which is the source of most arguments about the number.
How is market share by rooftop calculated?
Market share by rooftop = registrations attributed to the rooftop ÷ total registrations in the defined area and segment × 100
Three inputs decide what comes out:
- The area. Your PMA, a radius you drew, or the whole region. Widen the boundary and your share falls, every time, without anything changing on the ground.
- The segment. All light vehicles, your brand's competitive set, or one model line. Share of a segment you barely compete in is a vanity number.
- The attribution. Registrations are attributed by where the buyer lives, not where they bought. A car you sold to someone forty miles away counts in their area, not yours.
Market share by rooftop: a worked example
Take one franchised rooftop. In its PMA last quarter, 4,120 new light vehicles were registered in its competitive segment. 486 of those were its own brand. The rooftop itself sold 402.
Share of the total market is 402 ÷ 4,120, or 9.8 percent. Share of its own brand's registrations in its own area is 402 ÷ 486, or 82.7 percent. Both are correct, and they lead to opposite conversations.
The 84 cars of your brand registered in your PMA that you did not sell went to a sister store. That is the figure the field rep will lead with, and it is a different problem from the 3,634 registrations that went to other brands entirely. One is a conquest question. The other is a defence question, and no marketing budget fixes both at once.
Why the scale matters
According to NADA's 2025 data, 16,990 franchised light-vehicle dealers in the United States sold 16.2 million light vehicles, an average of roughly 950 new units per rooftop, at an average transaction price of 48,205 dollars. A single point of share in a busy PMA is worth more than most stores' entire annual advertising spend.
Urban Science, which builds its analysis on registration data, reported an average dealership defection rate of 20 percent in 2025 and found that 74 percent of dealers lack full visibility into where those defections go. Share is lost one customer at a time, mostly to stores the losing rooftop cannot name.
How the number gets misread
- Measured on the wrong geography. A rooftop that draws heavily from outside its PMA can be commercially healthy and look weak on the manufacturer's report. Both readings are real. Track both.
- Read as a marketing metric. Share responds to inventory mix, allocation and pricing before it responds to advertising. A store starved of the fast-moving trim will lose share while doing everything else right.
- Compared across rooftops with different PMAs. Population, income, brand strength and competitor density are not comparable between two sites in the same group. Rank rooftops against their own history, not against each other.
- Confused with volume. Unit sales can rise while share falls, when the whole market grew faster than you did. That is the pattern that gets missed in a good year.
- Lagged and treated as current. Registration data arrives weeks after the fact. By the time a share drop is visible, the cause is one or two months old.
- Divorced from the funnel. Share is an outcome. Closing ratio and appointment to sale ratio are the mechanisms that produce it, and they move first.
What a rooftop can actually control
Not the size of its PMA, not its allocation, and not what the store two junctions away decides to do on price. What it controls is the share of the opportunities that already reached it.
Which is why the most useful way to read a share decline is backwards. Start at defections inside the PMA, then the funnel conversions that produced them, then the process behind those. A share number on its own tells you that you lost. It never tells you where.
