Most teams treat the spec sheet as a checklist to clear once, then forget. That instinct costs money — because two of those spec decisions keep shaping delivery long after the campaign goes live.
The full spec sheet: file type, dimensions, character limits, card count
Here are the hard limits LinkedIn enforces on carousel ads as of 2025.
Card count: 2 minimum, 10 maximum per carousel ad.
Image format: JPG or PNG only. No GIF, no WebP, no SVG.
Minimum image dimensions: 1080x1080 px. LinkedIn will reject images below this threshold at upload.
Maximum file size: 10 MB per card.
Aspect ratios accepted: 1:1 (square), 4:5 (portrait), 1.91:1 (landscape). LinkedIn does not accept arbitrary ratios — the creative validator will flag anything outside these three.
Introductory headline: up to 255 characters. This is the text that appears above the carousel strip.
Card headline: up to 45 characters. This is the text that appears below each individual card image. Text beyond 45 characters is truncated in the feed — no ellipsis warning, just a hard cut.
Destination URL: required per card, HTTP or HTTPS only. Each card can point to a distinct URL.
CTA button: optional per card, selected from LinkedIn's fixed list (Download, Learn More, Register, Sign Up, etc.).
For the organic side of carousel mechanics, see LinkedIn Carousel : plus de dwell time, à une condition.
What is the best size for a LinkedIn carousel ad (and why 1080x1080 is the safe default)?
1080x1080 px at a 1:1 ratio is the lowest-risk choice for consistent rendering across placements.
LinkedIn's feed renders on screens ranging from a 6-inch phone to a 27-inch monitor. The 1:1 format occupies a predictable rectangle in both contexts. No cropping, no letterboxing, no unexpected reflow.
The 4:5 portrait format (1080x1350 px) captures more vertical screen space on mobile. That extra height can increase scroll-stop rate — the card physically takes up more of the visible viewport before a user swipes past. The trade-off: on desktop, LinkedIn may crop or compress the image to fit its feed column width, depending on placement.
The 1.91:1 landscape format (1200x627 px) is the weakest option for carousels. It was designed for single-image ads. In a carousel strip, landscape cards appear narrow and compete poorly for attention against square or portrait neighbors.
The practical rule: start with 1080x1080 px. Test 4:5 only if your creative team can produce assets natively at that ratio — not by cropping a square.
For templates that already respect these constraints, Canva LinkedIn Carousel Templates: Starting Point, Not Strategy covers what to adjust before you export.
The two spec decisions that change delivery, not just display
Aspect ratio and CTA URL structure are the two variables that move beyond visual formatting into auction behavior.
Aspect ratio affects real estate, which affects engagement signals. LinkedIn's auction weighs expected engagement rate when pricing impressions. A carousel that stops more thumbs — because it occupies more screen — generates stronger early engagement signals. Those signals feed back into the auction. A 4:5 card on mobile is not just taller: it is competing differently.
Per-card CTA URLs affect your ability to optimize. LinkedIn allows a distinct destination URL per card. If every card points to the same URL, you lose the ability to see which card drove which click. You cannot identify which message resonated, which visual converted, or where in the carousel sequence intent peaked.
More concretely: a carousel where card 3 drives 60% of clicks but all cards share one URL looks identical in your campaign dashboard to a carousel where clicks are evenly distributed. You cannot act on data you cannot see.
This is where the DSB Intelligence Recommendations Engine flags a pattern that technically passes LinkedIn's validator: a carousel with 8 cards, all pointing to the same landing page, no per-card UTM differentiation. The setup is spec-compliant. It is also analytically blind.
Common spec mistakes that waste budget before the first impression
Oversized files. A 9 MB PNG per card in a 10-card carousel means LinkedIn has to load up to 90 MB of creative before the first impression renders. On a slow mobile connection, that creative never loads. The impression is lost before the user sees anything. Compress to under 3 MB per card without visible quality loss — most image editors do this in one export step.
Truncated card headlines. The 45-character limit is tight. "Download our 2025 B2B Demand Generation Benchmark Report" is 57 characters. LinkedIn cuts it at 45, mid-word if necessary. The result looks broken in the feed. Write card headlines at 40 characters or fewer to leave a safe margin across all placements.
Mismatched aspect ratios across cards. LinkedIn requires all cards in a single carousel to share the same aspect ratio. Mixing a 1:1 card with a 4:5 card in the same ad is a validator error. The ad will not serve. This mistake appears most often when assets are sourced from multiple designers or repurposed from different campaigns.
No CTA button on high-intent cards. The CTA button is optional per card, but omitting it on cards that carry a direct offer (a demo request, a download, a pricing page) removes the most visible click target in the unit. Users who want to act have to click the card image itself — a smaller, less obvious target.
For a broader look at what separates high-performing carousel creative from the rest, LinkedIn Carousel Posts Examples: What Viral Ones Share breaks down the structural patterns. And if you are running video alongside carousels, LinkedIn Video Spec : ce que les specs ne disent pas covers the equivalent delivery-level decisions for that format.
On the agency side, LinkedIn Ads Management Services: What Agencies Get Wrong documents how spec errors compound when creative and media buying are handled by separate teams.
Et maintenant ?
- Audit your live carousel ads: check that every card headline is 45 characters or fewer, every image is under 3 MB, and every card has a distinct destination URL.
- If you are using landscape (1.91:1) images in a carousel, rebuild those assets at 1080x1080 px before your next campaign launch.
- Add per-card UTM parameters to every card URL so your analytics can attribute clicks at the card level, not just the ad level.
- Run your next carousel through a pre-flight check before it goes to LinkedIn's validator — catching truncation and file size issues before submission saves the back-and-forth.
Start a free trial of DSB Intelligence to flag spec issues and delivery-level misconfigurations before they cost you impressions.