Reddit Free-form Ads: Image Sizes, Text Limits and Thumbnail Rules

A Free-form Ad is an ad that looks like a regular Reddit post: a headline plus rich text with images and videos placed inside it. Other Reddit formats send the click to the advertiser's website. Here the click opens the post itself, and the links to your site sit inside the text.

There is one key difference in setup, and it is the thumbnail. For image, video and carousel ads, Reddit generates it automatically. For Free-form it does not. If you skip the thumbnail, your ad shows up in the feed with no media at all: just a headline and a few lines of text.

Below are the specs for every element: headline, body text, captions, images, videos and the thumbnail. All numbers come from the Reddit Ads help center.

How a Free-form Ad Works

A Free-form ad has two surfaces.

The first is the preview card in the feed. Reddit builds it from three parts: the thumbnail, the headline and the first lines of text. The full post never expands in the feed.

The second is the post page. It opens when the user clicks the preview card. Here the post shows in full: all the text with formatting, images, videos and the links you placed inside the text. The user reaches your website from here, on the second step.

This has a consequence for reporting: an ad click and a site visit are two different actions. Clicks in Ads Manager and sessions in your site analytics will diverge more than they do for an image ad, where the click goes straight to the site.

Comments are up to you. Turn them on, and a regular discussion thread appears under the ad.

There are two placements: feed and conversation. Reddit recommends running both so the ad shows across all placements.

One more instruction from the help center: build Free-form ads in Ads Manager instead of promoting an existing organic post. With promoted posts, the thumbnail may not display as expected.

Headline

The headline shows on both surfaces: in the preview card and on the post page. In the card it is the main text, the thing the user decides on before clicking.

Maximum length is 300 characters, though Reddit recommends staying under 100, and the safer limit is 80. One headline is required.

The gap between 300 and 80 characters is not about the limit, it is about truncation in the preview card. The help center says it directly: text gets cut off, and the result depends on the browser, the device and the font display size. The same headline shows in full on desktop and breaks mid-sentence on a phone with a large system font.

So 80 characters is not a style rule, it is insurance. If the meaning of your headline lives in the second half of the sentence, part of your audience will never see it.

Body Text

The body shows in full only on the post page. The preview card gets a fragment of the beginning: 3 to 6 lines.

Maximum length is 40,000 characters. One body is allowed, and it is not required.

The body is rich text: headings, lists, links, with images and videos between paragraphs. But all of that works on the post page. In the preview card, the fragment renders as plain text: headings, lists and links from the top of your post turn into ordinary lines.

The rest of the text never makes it into the card, no matter how much of it there is. The exact number of lines depends on the device and the font size, which is why the help center gives a range instead of a single number.

Hence the rule: the first lines of your post work as a second headline for the ad. Write them as plain continuous text, so they read without formatting and can break off without losing the point.

Captions for Images and Videos

Each image and video inside the post can carry a caption.

Maximum length is 50 characters, one caption per file, and captions are not required.

Captions live where the media lives, on the post page. Reddit's Free-form guide recommends using them: captions help walk the reader through a long post with several images and videos.

Images Inside the Post

Up to 20 files, in JPG, PNG or GIF, up to 10 MB per file, with a recommended minimum width of 1000 px.

Recommended resolutions:

• Square 1:1 — 1200 × 1200 px
• Landscape 4:3 — 1440 × 1080 px
• Landscape 16:9 — 1920 × 1080 px

You can upload an image of any aspect ratio, but the help center warns: non-standard ratios cause formatting discrepancies, such as letterboxing.

Note that there is no vertical format on this list. Portrait 4:5 in Free-form exists only for video.

If your image does not match the ratios, you do not have to rebuild it in an editor. Ad setup includes a Crop image tool: it changes the aspect ratio and crops the image right in the interface.

Videos Inside the Post

Up to 5 files, in MP4 or MOV (ProRes is not supported), up to 1 GB per file — though Reddit recommends keeping files to 50–100 MB — at up to 30 FPS, with a recommended length of 5–30 seconds.

Recommended resolutions:

• Square 1:1 — 1200 × 1200 px
• Portrait 4:5 — 1200 × 1500 px
• Landscape 4:3 — 1440 × 1080 px
• Landscape 16:9 — 1920 × 1080 px

The gap between the maximum and the recommended file size is not accidental. The help center warns that large files may not encode properly on upload. A 1 GB file will pass the limit, but the ad risks ending up with a broken video. Keep files under 100 MB.

Aspect ratios follow the same logic as images: any ratio is accepted, but non-standard ones break the layout. The resolution list here is one item longer: video gets Portrait 4:5, images do not.

Thumbnail

The thumbnail is the picture the user sees in the preview card in the feed. The interface marks this field as optional. Do not believe it: this is the most important field in the format.

File types are JPG or PNG, up to 3 MB.

Recommended resolutions:

• Landscape 4:3 — 400 × 300 px
• Square 1:1 — 300 × 300 px

For image, video and carousel ads, Reddit generates the thumbnail automatically from the uploaded media. For Free-form it does not, and the help center says so directly. Twenty images and five videos inside the post have no effect on the preview card: the thumbnail will not be pulled from there.

Leave the field empty, and the ad shows in the feed with no media at all: just a headline and lines of text. Formally, such an ad passes review and keeps running. In practice, it competes for attention in a visual feed without a picture.

So the rule is simple: optional by interface, required by outcome. The thumbnail gets uploaded every time.

Note the file type difference too: images inside the post accept GIF, the thumbnail takes only JPG and PNG.

The Aspect Ratio Labeling Error in Reddit's Help Center

Two values in the resolution tables above are labeled differently than in the help center. That is not a typo in this article, it is a correction of Reddit's error.

In the Free-form spec, the 1440 × 1080 px resolution is labeled Landscape 16:9. Check it by division: 1440 ÷ 1080 = 1.33. That is a 4:3 ratio. True 16:9 has a ratio of 1.78, and on this list it belongs to 1920 × 1080.

The same error appears in the thumbnail spec: 400 × 300 px is labeled Landscape 16:9, though 400 ÷ 300 = 1.33, which is 4:3 again.

That this is an error on the Free-form page specifically is visible from the neighboring sections of the help center: on the image ad and carousel ad pages, the same 1440 × 1080 resolution is labeled correctly as Landscape 4:3.

The practical takeaway: build your layouts from the pixel numbers, not the ratio labels. If a designer reads “16:9” and crops a 1440 × 1080 asset to fit that ratio, they will cut off part of the frame you meant to show.

Pre-launch Checklist

Five points where Free-form ads break most often.

1. The thumbnail is uploaded. Without it, the ad goes into the feed with no media.
2. The headline is under 80 characters. Or at least under 100: anything longer risks breaking off on phones.
3. The first 3–6 lines of the body read as plain text. Formatting does not work in the preview card, so the post cannot open with a list or a subheading.
4. Resolutions are taken from the pixel list, not from the ratio labels. Non-standard ratios produce letterboxing.
5. Videos are under 100 MB. A 1 GB file passes the limit but may fail to encode.

Everything else in this format forgives mistakes: text can be rewritten, images inside the post replaced, comments switched off. These five points get checked before launch, because each of them breaks the ad silently: no rejection from review, no error in the interface.