Thumbnail problems
Wrong thumbnail or cover: what each platform shows
Short answer
"Wrong thumbnail" is four different problems with four different fixes. The shape is wrong for the placement, so the platform crops or pads it. The image is right but unreadable at the size it is shown. The preview is stale because a platform caches it. Or the image was rejected outright: YouTube rejects custom thumbnails that break its Community Guidelines and can strike the account. Start with the published numbers for the platform you post on, then judge readability at the real display size.
Key takeaways
- YouTube publishes thumbnail numbers: 3840 × 2160 recommended for videos, 2160 × 3840 for Shorts, minimum width or height of 640 px.
- Custom thumbnails for Shorts can only be added in YouTube Studio on a computer, and the account must be verified.
- Instagram recommends a Reel cover of 420 × 654 and states you cannot edit it after uploading.
- TikTok's cover is a frame of the video, not an uploaded image: its API takes a millisecond offset and falls back to the first frame.
- LinkedIn's help does not document a cover image, so the first seconds of framing are the lever its documentation supports.
What each platform publishes about the preview image
The word thumbnail means three different things. YouTube publishes exact numbers for video and Short thumbnails. Pinterest documents a cover you choose when you create a video Pin, and publishes the ratio it recommends. Instagram publishes a recommended Reel cover size and says you cannot change it afterwards. TikTok documents a cover that is a frame of your video, not an image you upload. LinkedIn publishes nothing about a cover image for organic video posts.
| Platform | What is published | What is not published |
|---|---|---|
| YouTube video | 3840 × 2160 recommended, minimum width 640 px, 16:9 | Nothing more specific |
| YouTube Shorts | 2160 × 3840 recommended, minimum height 640 px, 9:16, Studio on a computer, verified account | Mobile upload of a custom Short thumbnail |
| Pinterest video Pin | 9:16 (1080 × 1920) recommended for full bleed, plus 1:1, 2:3, 3:4, 4:5, 1:2 | A minimum cover image size |
| Instagram Reel | Cover photo 420 × 654 (1:1.55), and it cannot be edited after upload | How the cover is cropped elsewhere |
| TikTok | The cover is a frame, chosen in milliseconds; the first frame by default | Uploading a cover image for a video post |
| Aspect ratio 1:2.4 to 2.4:1, resolution 256 × 144 to 4096 × 2304 | Any cover image or thumbnail for a video |
Everything in the third column is an absence in the platform's own help pages, checked on the date shown in Sources. Where a number is not published, this site does not invent one.
Find your case
| What you see | What it usually means | Do this |
|---|---|---|
| Preview is cut off at the top and bottom | The image ratio does not match the placement | Export at the published ratio for that platform (step 1) |
| Preview looks right but is hard to read | Too much detail at the displayed size | Fewer words, larger type, tested at real size (step 2) |
| Old image still showing after a change | The platform is still propagating the change | Wait and re-check the surface (step 4) |
| Thumbnail rejected or replaced | Policy or eligibility, not pixels | Read the published rules for that platform (step 5) |
| You cannot find the thumbnail option at all | The account or device is not eligible | Check the eligibility the platform documents (step 5) |
| Cover looks right in the app, wrong in the feed | Different surfaces crop differently | Keep the subject in the center and clear of the edges (step 3) |
Fix it step by step
Export at the ratio the platform publishes
YouTube: 16:9 for videos, 9:16 for Shorts, 3840 × 2160 and 2160 × 3840 recommended. Pinterest: 9:16 or 1080 × 1920 recommended for full-bleed video Pins, with 1:1, 2:3, 3:4, 4:5 and 1:2 also listed. Instagram Reels: a cover photo of 420 × 654, which is a 1:1.55 ratio.
Judge readability at the size it is shown
A thumbnail is often shown a few hundred pixels wide. Put your candidate next to the size it will appear at, then read it from arm's length: if the title needs effort, it is too long. YouTube's own A/B testing note adds a technical floor: if any thumbnail in a test is below 1280 × 720, every experiment thumbnail is downscaled to 854 × 480.
Keep the subject clear of the edges
Meta's safe-zone guidance for 9:16 creative says to keep the edges free of key elements, text and logos so they are not cropped out or covered by the user interface. Pinterest publishes the same idea as numbers: safe zones of top 270 px, left 65 px, right 195 px and bottom 790 px on its recommended Pin canvas.
Expect a delay before a new preview shows everywhere
YouTube says it may take time for thumbnail changes to appear. Instagram says you cannot edit a Reel cover photo after uploading it, so a change means a re-upload. Check the surface people actually use before you assume the change failed.
Read the eligibility and policy rules first
YouTube requires a verified account for custom thumbnails and, for Shorts, only allows them in YouTube Studio on a computer. It also publishes rejection categories and says repeat offences can remove the custom thumbnail privilege for 30 days or lead to account termination, and that there is a daily upload limit per channel.
Resize the image rather than scaling it by eye
Export at the target pixel size so the platform has nothing to guess:
ffmpeg -i clip.mp4 -ss 00:00:03 -frames:v 1 -q:v 2 cover.jpg, or resize the finished image file. Scaling up a small thumbnail adds no detail; it only makes the file heavier.
Published preview-image values, by platform
| YouTube video | 3840 × 2160 recommended, 16:9, minimum width 640 px · JPG or PNG |
|---|---|
| YouTube Shorts | 2160 × 3840 recommended, 9:16, minimum height 640 px |
| YouTube file size | 2 MB on mobile, 50 MB on desktop |
| Pinterest video Pin | 9:16 (1080 × 1920) recommended, or 1:1, 2:3, 3:4, 4:5, 1:2 |
| Instagram Reel cover | 420 × 654 (1:1.55), cannot be edited after upload |
| TikTok cover | A frame of the video; the first frame by default |
| Not documented · video aspect ratio 1:2.4 to 2.4:1 is published |
Two surfaces, two crops
YouTube documents one behavior that surprises people: vertical videos with a 16:9 custom thumbnail are replaced by an auto-generated 4:5 thumbnail on the home, explore and subscription pages, while the custom thumbnail still appears on the watch feed, watch history and non-mobile platforms. The same upload, two different previews.
Meta documents the same class of problem for creative: on screens taller than 9:16 it may either zoom the creative to fill the whole screen or show it in its original 9:16 with a black background. Neither is a bug; both are choices the platform makes.
Practical consequence: keep the important part of the image in the middle of the frame, so every one of those variants still reads.
Frequently asked questions
Why is my thumbnail cut off?
The image ratio does not match the placement, so the platform crops or pads it. Export at the ratio the platform publishes: 16:9 for YouTube videos, 9:16 for Shorts, 9:16 or 1080 × 1920 for full-bleed Pinterest video Pins.
Why can I not set a custom thumbnail on a Short?
YouTube documents that custom thumbnails for Shorts can only be added in YouTube Studio on a computer and that the account must be verified. On a phone the option is not there.
Can I upload my own cover image for a TikTok video?
TikTok's developer documentation treats the cover as a frame of the video: video_cover_timestamp_ms specifies which frame is used, and if it is not set or is invalid the cover is the first frame. No cover image upload is documented for video posts.
Why did my thumbnail get replaced?
YouTube publishes rejection categories for custom thumbnails and can strike the account, and it also replaces a 16:9 custom thumbnail on a vertical video with an auto-generated 4:5 thumbnail on the home, explore and subscription pages.
Do I need a minimum size for a thumbnail?
YouTube publishes minimums: a minimum width of 640 px for videos and a minimum height of 640 px for Shorts, with 3840 × 2160 and 2160 × 3840 recommended. Other platforms publish recommendations rather than minimums.
Sources
- YouTube Help: Add custom thumbnails on YouTube (official, checked 2026-10-07)
- YouTube Help: A/B test titles & thumbnails (official, checked 2026-10-07)
- Pinterest Help: Review Pin specs (Video Pin specs and safe zones) (official, checked 2026-10-07)
- Instagram Help: Reel size & aspect ratios (official, checked 2026-10-07)
- TikTok for Developers: Content Posting API reference (video_cover_timestamp_ms) (official, checked 2026-10-07)
- LinkedIn Help: Video sharing troubleshooting (formats, limits, safe zones) (official, checked 2026-10-07)
- Meta Business Help: About text overlays and the safe zone for ads (official, checked 2026-10-07)
- FFmpeg Documentation: Command line options (-map, -c copy, -itsoffset) (official, checked 2026-10-07)
Reviewed 2026-10-07. Steps not attributed to a source are general video practice or computed above.