Reddit Ad Specs 2026: The Complete Sizing Reference

This is a complete reddit ad specs reference: every dimension, file size, format, and character limit across image, video, carousel, and text ads, pulled from Reddit's own advertising documentation and cross-checked against current ad-manager behavior. No filler, no guessing on numbers. If a spec wasn't confirmed by a source we trust, it's not in here.

Reddit updates these specs often enough that a two-year-old blog post is a liability, not a resource. This one is current as of July 2026 and links back to Reddit's official ad-unit documentation so you can verify anything before you build.

Most spec pages ranking for this term right now either miss an ad type entirely, mix up dimensions across formats, or cite numbers with no source at all. That's the gap this page is built to close: every number below either links to Reddit's own documentation or is flagged as a range where sources genuinely disagree, so you're not guessing at upload time.

Reddit ad specs: quick reference table

Ad type	Dimensions	Max file size	Format	Headline limit
Image ad	1080×1080 (1:1), 1080×1350 (4:5), 1920×1080 (16:9)	3 MB (up to 20 MB accepted on some placements)	JPG, PNG, GIF	300 chars (Reddit recommends under 100)
Video ad	1200×1200 (1:1), 1200×1500 (4:5), 1920×1080 (16:9), 1440×1080 (4:3)	1 GB (512 MB recommended)	MP4, MOV	300 chars (Reddit recommends under 100)
Carousel ad	2 to 6 cards, consistent aspect ratio per card	20 MB per image (3 MB per GIF)	JPG, PNG, GIF	300 chars overall; ~50 char captions per card
Text / free-form ad	No image required (placeholder shown if omitted)	Images up to 10 MB each (max 20 files); video up to 1 GB (max 5 files)	JPG, PNG, GIF, MP4, MOV	Body up to 40,000 chars

Treat this table as the starting point, then read the section for your ad type below, because the placement (feed vs. conversation) and card-level rules change some of these numbers.

Image ad specs

Image ads are still the default building block of most Reddit campaigns: one static image, a headline, and a link.

Dimensions. Reddit supports three main aspect ratios for image ads: 1080×1080 (square, 1:1), 1080×1350 (portrait, 4:5), and 1920×1080 (landscape, 16:9), per Reddit's ad unit specifications. Portrait and square perform better on mobile simply because more of Reddit's traffic is mobile, and those ratios fill more of the screen without the ad getting cropped.

File format and size. JPG, PNG, and GIF are accepted formats. The commonly cited cap is 3 MB for the primary image, though Reddit's upload tooling in some placements will accept larger files up to roughly 20 MB before flagging a warning, according to Reddit's help documentation. If you're building assets from scratch, target under 3 MB and you won't have to think about it.

Thumbnail. For compact and conversation-style placements, Reddit falls back to a smaller thumbnail image: 400×300 (4:3 aspect ratio), capped at 500 KB. If you don't supply one, Reddit will crop your primary image down, and crops on Reddit's automated system are not always flattering to text-heavy creative.

Headline. The hard cap is 300 characters, but Reddit's own guidance recommends staying well under 100. In practice, headlines that read like an actual Reddit post title (lowercase, conversational, no marketing verbs) outperform anything that looks like ad copy. That's a content decision, not a spec, but it's worth stating next to the number because the number alone will mislead you into writing something too long.

Minimum resolution. Reddit's documentation also sets a floor, not just a ceiling: images below roughly 600px on the shortest side get rejected or flagged at upload. If you're pulling stock creative or resizing an existing brand asset down for Reddit, check the output dimensions before you upload rather than after the campaign is already flagged for review.

Safe zones. Reddit doesn't publish a strict pixel-for-pixel safe zone the way some platforms do, but the practical guidance from agencies running high creative volume on the platform is consistent: keep essential text and faces centered in the top two-thirds of the frame, and treat the bottom fifth of the image as expendable. Compact and conversation placements crop more aggressively than the full feed view, and that crop tends to eat the bottom of the frame first.

Video ad specs

Video is where Reddit's spec sheet gets the most inconsistent across third-party write-ups, so treat the ranges below as the safest common ground.

Dimensions. Reddit supports 1:1 (1200×1200), 4:5 portrait (1200×1500), 16:9 landscape (1920×1080), and 4:3 (1440×1080). As with images, portrait and square are the mobile-friendly defaults.

File format and size. MP4 or MOV, up to 1 GB, with 512 MB recommended for faster processing and fewer upload failures on slower connections.

Length. Reddit's technical ceiling is generous, up to 15 minutes in most placements. That does not mean 15 minutes is a good idea. Every credible source on this converges on the same practical range: 5 to 30 seconds performs best for feed placements, with completion rates dropping off sharply past the 30-second mark unless the content is genuinely built to hold attention (tutorials, demos with a hook up front).

Frame rate. 30 FPS maximum.

Captions. Not technically required, but functionally mandatory. Reddit video ads autoplay muted by default, and a user has to tap to unmute. If your message depends on audio and you have no on-screen captions or text overlay, most viewers never get the message at all. Burned-in captions or Reddit's caption upload option both work; either beats nothing.

Thumbnail. Same as image ads: 400×300, JPG or PNG, under 500 KB, used for compact and conversation placements.

Carousel ad specs

Carousel ads let you run 2 to 6 swipeable cards in a single unit, each with its own image or GIF and a short caption.

Card count. Minimum 2, maximum 6 cards per carousel.

File size and format. JPG, PNG, or GIF. Static images can run up to roughly 20 MB per card; GIFs are capped lower, around 3 MB, because Reddit has to keep the whole carousel loading fast on mobile data.

Consistency. Reddit recommends (it isn't strictly enforced, but it matters for how the unit renders) keeping the same aspect ratio across every card in a carousel, whether that's 4:5 portrait, 4:3, or 16:9. Mixed ratios within one carousel create visible letterboxing between cards as a user swipes, which looks broken even when it technically isn't.

Text limits. The overall headline follows the same 300-character ceiling as image ads (recommended under 100), and each individual card caption is limited to roughly 50 characters. That's tight enough that you're writing a label, not a sentence, for each card.

Text and free-form ad specs

Text ads are the closest thing Reddit has to a native post as an ad unit: no image is required, and if you don't upload one, Reddit shows a placeholder so the post still renders correctly in-feed.

Free-form ads (Reddit's format for longer-form, post-style ad content) support up to 20 image files (JPG, PNG, or GIF, max 10 MB each) and up to 5 video files (MP4 or MOV, max 1 GB each), plus a required thumbnail (JPG or PNG, under 3 MB) if video is included.

Body text. Up to 40,000 characters, which is effectively no limit for any realistic ad copy. That said, shorter, more native-feeling body text consistently outperforms long-form ad copy in Reddit's feed environment, because the format's whole advantage is that it doesn't look like an ad.

Character limits by placement. Feed placements generally allow longer headlines to render fully (Reddit cites up to 150 characters before truncation in some feed contexts), while the more compact conversation placement truncates closer to 100 characters. When in doubt, write for the shorter limit so your headline reads the same everywhere it shows up.

Reddit-specific rules that aren't in the size chart

A few rules matter as much as the pixel dimensions and don't show up in most spec sheets:

• The "Promoted" tag is non-removable. Every Reddit ad carries a visible promoted label. You cannot disguise an ad as an organic post, and attempts to mimic community tone in a way that's deceptive (fake usernames, manufactured engagement) are grounds for account termination under Reddit's advertising policy.
• AI-generated creative disclosure. Reddit's advertising policy requires advertisers to disclose when ad creative, whether image, video, or copy, is substantially AI-generated.
• Testimonials must be real. Any review or testimonial used in ad copy has to be genuine and verifiable. Fabricated or compensated-but-undisclosed endorsements violate both Reddit's policy and FTC guidelines, and Reddit enforces this on the ad side, not just organically.
• Comment moderation is limited. Advertisers running ads that accept comments cannot delete legitimate criticism just because it's unflattering. Moderation has to follow Reddit's content policy, not brand preference.

None of this is exotic, but it's exactly the kind of rule that gets an account suspended mid-campaign when nobody on the creative team knew it existed. Spec compliance gets your ad approved. Policy compliance is what keeps the account running long enough for that ad to actually spend a budget.

Why third-party spec pages disagree with each other

If you've searched this before landing here, you've probably noticed that different sites quote different numbers for the same ad type, sometimes the file size cap, sometimes the video length ceiling. Part of that is genuine platform change: Reddit adjusts ad-manager tooling more often than it publishes changelog notes, so a spec that was accurate six months ago can drift without warning. Part of it is that older posts get updated with a new date stamp but not new research underneath.

The practical fix is the same one Reddit itself recommends: treat any written spec sheet, including this one, as a strong starting point, and let the Ads Manager upload flow be the final word. It will reject a file that's too large or the wrong dimension before it lets you publish, which is the one signal that's always current.

FAQ

What's the maximum file size for a Reddit image ad?

3 MB is the commonly enforced cap for the primary image, though some upload flows tolerate larger files before flagging an error. Build to 3 MB and you avoid the issue entirely.

How long can a Reddit video ad be?

Up to 15 minutes technically, but 5 to 30 seconds is the practical range that holds attention and gets the best completion rates in feed placements.

Does Reddit require captions on video ads?

Not as a hard technical requirement, but functionally yes, since video autoplays muted and most viewers never tap to unmute.

How many cards can a Reddit carousel ad have?

Between 2 and 6, each with its own image or GIF and a caption capped around 50 characters.

If the ads aren't the problem, the channel might still be right

Specs get an ad approved. They don't make Reddit users trust a brand, and paid Reddit placements live or die on how native they feel to the platform, which is a harder problem than any dimension chart solves.

Related reading

• Reddit Ads Cost in 2026: Real CPM, CPC & Budget Data
• How to Create a Subreddit for Your Brand (2026)
• The Reddit marketing guide

If you've run Reddit ads and the numbers didn't work, it's worth asking whether the issue was the creative or the channel strategy underneath it. subredditmarketing.com runs the organic side of Reddit as a full channel for funded B2B SaaS, fintech, and DTC brands: real account participation, subreddit-native posts and comments, and lead generation that doesn't depend on an ad budget at all. If you want to talk through what that looks like for your brand, book a call with Subreddit Marketing.