Reddit Specifications

Post Image

Dimensions	Up to 4000 × 4000 px
Aspect Ratio	Any (1.91:1 recommended for feed display)
Max File Size	20 MB
File Formats	JPG, PNG, GIF
Notes	Gallery posts support up to 20 images

Gallery Post

Dimensions	Up to 4000 × 4000 px per image
Max File Size	20 MB per image
File Formats	JPG, PNG, GIF
Notes	Up to 20 images; each can have its own caption (180 characters). Corroborated this pass by a second independent source — Social Media Today's coverage of the gallery-post feature launch quotes verbatim: "add an optional caption (up to 180 characters) or URL for each image". Treated as confirmed

Post Video

Aspect Ratio	Any; 16:9 displays best
Max File Size	1 GB
File Formats	MP4, MOV
Resolution	1920 × 1080 px recommended
Max Duration	Up to 15 minutes
Notes	H.264 codec; audio optional but supported; GIF-style looping also available

Post Title

Character Limit	300 characters
Notes	Required; shown in feed and search results

Post Body (Text)

Character Limit	40,000 characters
Notes	Rich text editor; supports Markdown formatting

Comment

Character Limit	10,000 characters

Profile Bio

Character Limit	200 characters

Username

Character Limit	20 characters
Notes	Cannot be changed after creation

Subreddit Name

Character Limit	21 characters

Avatar

Dimensions	256 × 256 px minimum
Max File Size	10 MB
File Formats	JPG, PNG
Notes	Displayed as a circle

Profile Banner

Dimensions	1920 × 384 px recommended (5:1)
Max File Size	10 MB
File Formats	JPG, PNG
Notes	Secondary sources disagree on exact recommended size (1920×384, 1200×400, 1600×480, and 1000×300 all cited by different guides); center-third is the safe zone since edges crop on narrow screens. Re-attempted this pass via a working route into Reddit's official Zendesk help API (support.reddithelp.com, which 403s on direct fetch but is reachable through a reader proxy) — searched and read Reddit's full Profiles help section (all 5 articles, including "How do I update my profile settings?" and "How do I update my avatar image?") in full. Confirmed: Reddit's official Help Center has no dedicated article for the user PROFILE banner and states no pixel dimensions for it anywhere — only the separate SUBREDDIT/community banner has an official spec article. This is a genuine gap in Reddit's own documentation, not just a fetch-blocking issue; the dimension figure remains a secondary-source estimate

Subreddit Icon

Dimensions	300 × 300 px
Max File Size	500 KB
File Formats	JPG, PNG
Notes	Displayed as a circle

Subreddit Banner

Dimensions	At least 1072 × 128 px (desktop); at least 1080 × 128 px (mobile)
Max File Size	10 MB
File Formats	JPG, PNG
Notes	Desktop and mobile banners are uploaded separately in mod tools; 1080 × 128 px recommended for mobile

Promoted Post (Image)

Dimensions	1440 × 1080 px (4:3) recommended cross-device; mobile also 1:1 1080×1080, 3:4 1080×1440, 4:5 1080×1350 and 16:9; desktop 4:3 or 16:9 1920×1080
Max File Size	3 MB
File Formats	JPG, PNG, GIF
Notes	Per Reddit's official image ad specifications; headline up to 300 characters

Promoted Post (Video)

Max File Size	1 GB
File Formats	MP4, MOV
Resolution	1440 × 1080 px (4:3) or 1920 × 1080 px (16:9) cross-device; mobile also 1:1 1200×1200, 3:4 900×1200, 4:5 1200×1500
Max Duration	2 seconds to 15 minutes
Notes	Maximum 30 fps; ProRes not supported

Carousel Ad

Dimensions	1200 × 1500 px (4:5), 1440 × 1080 px (4:3) or 1920 × 1080 px (16:9) cross-device; 1200 × 1200 px square also accepted
Max File Size	20 MB per card (static); 3 MB per card (GIF)
File Formats	JPG, PNG, GIF
Notes	2–6 cards per carousel; per-card caption up to 50 characters; file size limits confirmed on Reddit's official carousel ad specifications

Ad Headline

Character Limit	300 characters

Ad Body

Character Limit	500 characters