Reddit Image Ads: Image Sizes, Aspect Ratios and Thumbnail Specs

An image ad is the simplest format in Reddit Ads: a headline, one image, a link to your site.

Simple only at the setup stage. You upload one image, but it shows up in three places, and not in full everywhere. The card view in the feed shows the whole image. The compact view and the conversation placement show a thumbnail with a 4:3 ratio instead.

So the size you export is not a matter of taste. It depends on where the ad will run. Below are the requirements for every element of an image ad: headline, links and button, image file, sizes by device, and thumbnail. All numbers come from the Reddit Ads help center.

How an Image Ad Is Displayed

Reddit ads have two placements. Feed covers the Home page, Popular, and individual community feeds. Conversation means the ad shows inside the comment thread under a post. Reddit recommends turning on both so the ad picks up every impression available.

The feed has two view modes, and the user switches between them in their own account settings. Card view shows the image at full size under the headline. Compact view collapses the post down to a headline with a small image next to it.

That decides which file a person actually sees. Card view shows your uploaded image. Compact view and the conversation placement show the thumbnail. It has its own requirements, covered below.

Clicking the image opens your destination URL. Comments under the ad are turned on with a toggle in the setup.

Headline

The headline is required and holds up to 300 characters. Reddit recommends no more than 100 characters, or no more than 80 if truncation is a concern.

Truncation depends on the browser, the device, and the user's font size setting. All three sit on the reader's side, so there is no way to calculate the cutoff point in advance. The same headline breaks in different places for different people.

That gives you a working rule: fit the meaning into the first 80 characters and treat the rest as an add-on that part of your audience will never see.

Links and Button

Destination URL. Required, up to 268 characters. This is the address that opens on click.

Display URL. Up to 100 characters. The domain has to match the domain of your destination URL. If the ad points to example.com, you cannot show shop.example.net in this field.

Call to action. You pick the button text from a preset list in the ad setup. Custom text is not an option.

The 268-character limit looks like plenty of room, but UTM tags eat through it faster than expected. This URL takes 175 of the 268:

https://example.com/landing-page/summer-sale?utm_source=reddit&utm_medium=cpc&utm_campaign=summer_sale_2026_us_prospecting&utm_content=image_ad_1080x1350_v3&utm_term=r_gadgets

The domain here is short, the path is short, and the campaign and creative names are ordinary. Add a long product path or a tracker's parameters and the limit turns into a real constraint.

Image File

File types are JPG, PNG, or GIF, up to 3 MB, and any aspect ratio is accepted.

That last one comes with a catch. Reddit accepts a file at any aspect ratio, but non-recommended ratios cause letterboxing: the image fits inside the display area and empty bars are left along the edges. The ad is not rejected for it, and no error shows up in the interface.

Within the accepted ratios, the help center advises using the highest resolution you have. Quality holds up better on large screens, and 3 MB leaves room to spare.

If you do not have a file in the ratio you need, the ad setup includes a Crop image tool. It changes the aspect ratio and crops the uploaded image without an outside editor.

Sizes by Device

The help center splits the recommended sizes into three sets.

Cross-device. Reddit recommends using a single Landscape 4:3 image at 1440 × 1080 px across all devices, placements, and view modes — the only ratio that appears in both the mobile and the desktop list.

Mobile. Recommended ratios:

• Square 1:1 — 1080 × 1080 px
• Portrait 3:4 — 1080 × 1440 px
• Portrait 4:5 — 1080 × 1350 px
• Landscape 4:3 — 1440 × 1080 px
• Landscape 16:9 — 1920 × 1080 px

Desktop. Recommended ratios are Landscape 4:3 (1440 × 1080 px) and Landscape 16:9 (1920 × 1080 px).

The help center adds a separate list of acceptable ratios for desktop: Square 1:1 (1080 × 1080 px) and Portrait 3:4 (1080 × 1440 px). Acceptable, not recommended, which means letterboxing is possible.

Those three sets point to one practical limit. There are no portrait ratios in the desktop recommendations. Portrait 4:5 and 3:4 stay a mobile thing, and if your campaign runs on both devices, a vertical creative gets bars on the sides in the desktop feed.

Thumbnail

The thumbnail shows up only in the conversation placement and in compact view. Card view does not use it.

Reddit generates the thumbnail automatically from the ad's main image. You can upload your own file instead, and the uploaded one can be cropped in the interface as well.

File types are JPG, PNG, or GIF (a GIF is converted to a still image), up to 3 MB.

Recommended resolution is Landscape 4:3 at 400 × 300 px. Acceptable resolutions are Square 1:1 (300 × 300 px) and Landscape 16:9 (400 × 225 px).

The help center warns that a thumbnail in these or any other ratios may cause formatting discrepancies.

What follows next comes from the mechanics, not from the help center. The automatic thumbnail is built from the main image, and the recommended thumbnail ratios are horizontal. So a vertical 4:5 or 3:4 creative loses part of the frame at the top and the bottom during automatic generation. You do not get to choose what stays.

How to Show a Different Image in Conversations

The help center frames thumbnail replacement as more than a fix for automatic cropping. It is the standard way to set a separate image for the conversation placement and compact view.

That gives you two creatives inside one ad: the main one for card view and a separate one for the other two display surfaces.

When it is worth doing:

The main image is vertical. The automatic 4:3 thumbnail will cut off the top and bottom.

There is text in the frame. At 400 × 300 px only large type stays readable — small text from the main layout turns into unreadable lines.

The composition rests on one detail. If the point of the shot is a single small object, it gets lost in the thumbnail.

A replaced thumbnail is cropped right in the ad setup, so you do not have to prepare a separate file at the exact size.

Pre-launch Checklist

Five items, each of which breaks the ad without any error message.

1. The point of the headline fits in the first 80 characters. The cutoff depends on the browser and the user's settings, and there is no way to predict it.
2. The display URL domain matches the destination domain. A subdomain or a different zone does not count as a match.
3. The file is under 3 MB.
4. The aspect ratio comes from the recommended list. Any other ratio is accepted, but it leaves bars along the edges.
5. The thumbnail has been looked at. The automatic one is built from the main image, and it will crop a vertical frame.

The first four can be checked before upload, in the file and against the table. The fifth one only works in the interface: until the main image is uploaded, there is no thumbnail to look at.