DOOH vs paid social

The short answer

The CPMs are not the same unit. A digital billboard CPM of $5-$18 AdQuick 2026 prices estimated passing exposures under Geopath methodology Geopath Ongoing; a social CPM prices individually served, viewable placements with user-level frequency caps. Comparing the two numbers raw flatters DOOH; state both definitions in the deck and compare outcomes instead.

Where DOOH wins

Attention quality: a 14:48 face at an interchange cannot be scrolled past, blocked, or skipped.
Brand safety: your creative appears next to a highway, not user-generated anything.
No fatigue mechanics: no frequency caps burning out an audience segment; the board hits everyone who passes, daily.
Credibility signal: physical presence reads as substance; the industry sells this as the trust effect, and OAAA's effectiveness studies live here OAAA FY2025.

Where social wins

Attribution: click-through and conversion tracking exist; DOOH attribution is modeled footfall and lift studies with honest limits (measurement).
Targeting: person-level audiences vs location-level ones.
Iteration speed: hundreds of creative variants tested in days; a billboard tests one message per slot.

The support-channel framing

The defensible 2026 posture: DOOH as a support channel that lowers blended acquisition cost by boosting branded search and conversion rates on the channels that can measure them. If you are building that model, benchmark your channel CACs first; the cross-channel benchmark hub at averagecac.com is the reference desk we point to. Then size the DOOH slice with the planner so the support channel has a defensible number too.

What split does the evidence support?

No neutral body publishes an optimal split, and anyone quoting one is selling something. What is documented: US OOH grew to a record $9.46B in 2025 with digital at 36.3% OAAA FY2025, alongside social's continued growth; advertisers run both. Structure the test so each channel is judgeable (the $25k test attaches the measurement plan), then let your own lift data set the split. Related: is billboard advertising effective, the cost answer, the plan track.