# Upload a custom thumbnail for a YouTube video

By HeyMark · Updated October 16, 2026

This guide covers **long-form videos**, not Shorts. YouTube lets you upload a custom thumbnail from a video's details in Studio when the channel has access to the feature. Phone verification unlocks custom thumbnails, though YouTube may change access if the channel has restrictions for Community Guidelines or copyright strikes. ([YouTube Help: custom thumbnails](https://support.google.com/youtube/answer/72431?hl=en); [features with phone verification](https://support.google.com/youtube/answer/9722880?hl=en))

## Prepare the image

For videos, YouTube recommends **3840 × 2160 px**, at least **640 px wide**, a **16:9** aspect ratio, and an image format such as JPG or PNG. The file size limit depends on the upload device. Resolution and aspect ratio are recommendations, not file size limits. ([YouTube Help: image size and resolution](https://support.google.com/youtube/answer/72431?hl=en))

| What to check | YouTube recommendation or limit |
| --- | --- |
| Resolution | Recommended: 3840 × 2160 px; recommended minimum width: 640 px. |
| Aspect ratio | Recommended for videos: 16:9. |
| Format | Image formats such as JPG or PNG. |
| File size on desktop | Up to 50 MB for video thumbnails. |
| File size on mobile | Up to 2 MB for video thumbnails. |

If your image doesn't meet a recommendation, prepare a high-resolution 16:9 version. If it exceeds your device's file size limit, export a smaller image file; don't convert it to a video or document. YouTube presents 3840 × 2160 as a recommendation, not a strict upload requirement.

## Upload the thumbnail in Studio

1. Open [YouTube Studio](https://studio.youtube.com/) and sign in with the channel that manages the video.
2. In the left menu, select **Content** and open the details for the long-form video you want to edit.
3. Under **Thumbnail**, click **Upload file** and choose the image saved on your device.
4. Check the preview to make sure it is the right image, then click **Save**.
5. Return to the video details and confirm that the selected thumbnail appears there. YouTube notes that the change may take time to appear everywhere.

**Fictional example:** for a photography talk, you prepare a horizontal 3840 × 2160 JPG under 50 MB and assign it to the video from a computer. The chosen image appears in Studio's details after you save. This is an illustration, not a real upload.

## If you can't upload it or don't see the change

- **“Upload file” is missing:** confirm that you're on the details page for the right long-form video, then check **Settings → Channel → Feature eligibility**. Custom thumbnails require access to the feature, and eligibility can vary by channel. YouTube says phone verification unlocks it and that restrictions can affect access. Follow the status and instructions shown for your channel.
- **The file is rejected:** confirm that it's an image format Studio accepts, such as JPG or PNG, and that it's under 50 MB on desktop or 2 MB on mobile. Also check that it follows YouTube's Community Guidelines. If Studio reports a daily limit, try again later; YouTube says limits may vary by region or channel history.
- **You saved it but still see the old image:** confirm that the intended image appears in Studio's details and that you clicked **Save**. The update may take time to appear on YouTube, so check again later.
- **Your video is a Short:** follow the separate [YouTube Shorts thumbnail instructions](https://heymark.ai/en/solutions/youtube-shorts-thumbnail/); the aspect ratio and interface differ.

[YouTube's custom thumbnail guidance](https://support.google.com/youtube/answer/72431?hl=en) also explains content policies and daily limits. If someone else needs to make the change, review [YouTube channel permissions](https://heymark.ai/en/solutions/youtube-channel-permissions/) before sharing access.

If you have several options for a long-form video, you can [A/B test thumbnails in YouTube](https://heymark.ai/en/solutions/test-youtube-thumbnails/) and review the result before choosing.

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## Keep reading

- [Create and manage a YouTube playlist](https://heymark.ai/en/solutions/create-manage-youtube-playlist/): Create a YouTube playlist in Studio, choose who can view it, add videos, and reorder them. Check the account and playlist limits before sharing.
- [Change a YouTube Shorts thumbnail](https://heymark.ai/en/solutions/youtube-shorts-thumbnail/): Choose a frame in the YouTube app or upload an image in YouTube Studio on a computer. Check account verification and where the image may appear.
- [How to translate your YouTube video titles and descriptions](https://heymark.ai/en/solutions/translate-youtube-video-title-description/): Learn to add a translated title and description to your own YouTube videos. Follow the steps from your channel and check a Spanish-to-English example.

## Developer and agent resources

- [HeyMark MCP documentation](https://heymark.ai/en/mcp/)
- [llms.txt](https://heymark.ai/llms.txt)
- [Full site content for language models](https://heymark.ai/llms-full.txt)
- MCP protocol endpoint: `POST https://mcp.heymark.ai`
- OAuth protected-resource metadata: [/.well-known/oauth-protected-resource](https://mcp.heymark.ai/.well-known/oauth-protected-resource)
- MCP server card: [/server-card](https://mcp.heymark.ai/server-card)