OOH artwork specs: what every media owner actually wants

OOH artwork gets rejected for the same handful of reasons, over and over. None of them are creative — they're spec issues. Get the spec right and the file ships first time.

Here's what the major UK media owners actually want, distilled from the spec sheets they don't always make easy to find.

The headline rules

Across nearly every UK OOH media owner, the constants are:

• Build at 10% of final size (1:10 scale). A 48-sheet billboard at 6096 × 3048 mm is built at 609.6 × 304.8 mm.
• 300 dpi at that scale — which equates to 30 dpi at full size. That's enough at typical viewing distances.
• CMYK only. No RGB, no spot colours unless explicitly requested.
• PDF/X-1a or PDF/X-4 depending on the media owner.
• Fonts embedded or outlined. No live type.
• No crop marks, no registration marks inside the trim area.

If you only remember one thing: 10% scale, 300dpi, CMYK, PDF/X.

Bleed and safe area

Bleed varies. A six-sheet (1200 × 1800 mm) typically wants 5 mm bleed all round at full size — so 0.5 mm at 10% scale. A 48-sheet often wants 25 mm at full size.

Safe area matters more than people realise. On large formats, the panel edges often disappear behind a frame or are stretched onto a curve. Keep critical copy and logos well inside the safe zone — usually 100 mm clear at full size on a 48-sheet.

Check the spec sheet for the exact campaign panel. Always.

Resolution at scale

The 1:10 / 300dpi rule means linked images need to be at the right resolution at final print size, not at the document size.

The quick check: if you scale a placed image up to 1000% (to simulate full size), is it still sharp? If it pixelates, it'll pixelate on the billboard too.

Colour

OOH printing is forgiving on subtle gradients and merciless on rich brand colours. Two specifics:

• Total ink coverage — usually 240–280% for OOH substrates. Rich blacks built for litho (320%+) will smudge.
• Skin tones drift toward magenta on large-format inkjet. Build slightly cooler if you can.

If brand colour accuracy is critical (Coca-Cola red, Tiffany blue), ask the media owner whether they can run a spot match or a custom profile. Some can.

File format by media owner

Spec sheets change, so always check, but the common pattern in the UK:

• JCDecaux — PDF/X-1a, fonts outlined, 1:10 scale
• Clear Channel — PDF/X-1a or X-4, 1:10 scale
• Global — PDF/X-1a, 1:10 scale
• Ocean Outdoor (digital DOOH) — varies hugely by screen; often MP4 or JPEG at native screen resolution
• Transport for London (Tube/rail) — strict spec sheets per format, including readability and trademark rules

Digital OOH (DOOH)

A different game. Built at the screen's native pixel resolution, not 1:10. Common formats:

• 6-sheet digital: 1080 × 1920 px
• 48-sheet digital: 1400 × 700 px (varies)
• Large iconic screens: ask for the exact pixel spec — they're all bespoke

For animation, most networks accept 10-second loops, MP4 (H.264), under 10 MB. Some still want JPEG sequences. The spec sheet is the only source of truth.

What gets files rejected

In rough order of frequency:

1. Built at full size instead of 1:10 (file is enormous, dpi is wrong)
2. RGB images sneaking in
3. Fonts not embedded or outlined
4. Bleed missing or wrong size
5. Total ink coverage too high
6. Wrong PDF standard

All of these are caught by a proper pre-flight before delivery. None of them are caught by "looks fine on screen".

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Need OOH artwork that lands first time at JCDecaux, Clear Channel or any UK media owner? Get in touch — we've shipped to all of them.