How will a thumbnail look in YouTube’s feed, search and sidebar?

What YouTube says about where a thumbnail appears

From YouTube’s page on custom thumbnails, read on 11 October 2026:

• The thumbnail is used as the preview image in the embedded player.
• Vertical videos with 16:9 custom thumbnails are replaced by an auto-generated 4:5 thumbnail on the home, explore and subscription pages. The custom thumbnail still appears on the watch feed, in watch history and on non-mobile platforms.
• Custom thumbnails need a verified account, and Shorts thumbnails can only be added in YouTube Studio on a computer.

YouTube’s thumbnail and title tips add that thumbnails show up differently across devices, so the image should be as large as possible, and that viewers may only see part of a title, so the important words go first. The page measures success by click-through rate on Home and Suggested in the first 24 hours for general audiences, and in the subscriptions feed for subscribers.

Neither page describes a preview of how a thumbnail will look in the feed. Studio lets you upload, save and, on a computer, A/B test.

The sizes we measured

On 11 October 2026 we measured the thumbnails YouTube drew on youtube.com in a desktop browser window 1400 pixels wide:

The three long-video places are 16:9 (1.78), the shape YouTube’s page asks of a thumbnail. The Shorts shelf in search results used a 2:3 tile, not 9:16. These sizes move with the window and the device: a phone, a TV and a narrow window each draw it differently, so treat the table as a reading, not a specification. What does not change is the order of size: the list beside a playing video is the smallest of the three 16:9 places, and a thumbnail that holds up there holds up elsewhere.

What a preview can and cannot tell you

A preview can show you:

• Whether it reads small. One subject and a few words at the narrowest size. Fine print and small logos go first.
• How it sits in light and dark. An edge that matches a page’s background melts into it.
• How it stands among neighbours. Placed in a row of other videos’ thumbnails, a bold one can turn out to look like all the others.

A preview cannot show you:

• Whether people click it. Click-through is what YouTube’s own tips measure, in Analytics, after publishing.
• The 4:5 thumbnail YouTube generates for vertical videos on the home, explore and subscription pages, which is not your image.
• How a title is cut, which depends on the width of the surface and the device.
• Other devices. A TV or a phone in landscape is a different size again.

Letting YouTube pick the winner

YouTube Studio’s A/B test shows up to 3 titles and thumbnails to viewers and keeps the one with the highest watch time; if there is no clear winner, the first one you uploaded stays. It is available on computers only, needs advanced features enabled, and does not work for Shorts, scheduled lives or premieres. A test should finish within two weeks. The page also says that if any test thumbnail is below 720p (1280 × 720), all of them are downscaled to 480p (854 × 480), so upload each at 3840 × 2160 or at least 1280 × 720. Use a preview to decide which three deserve the test.

What the free thumbnail tester does

The YouTube thumbnail tester draws your thumbnail, with a title, a channel name and a length you type, in a home-feed card, a search result, a narrow list entry and a phone-width card, in YouTube’s light and dark themes. It checks the image against the requirements on YouTube’s help page, lets you add up to three other videos’ thumbnails by link or file to compare, and exports a copy at 1280 × 720 under 2 MB or at full size under 50 MB. Your image stays in the page; a thumbnail added by link loads from YouTube’s image server, so YouTube sees that request.

Its cards use fixed widths, from 168 to 360 pixels and up to 390 for the phone card, and the narrowest is smaller than the 235 pixels we measured at 1400 pixels, so it shows the thumbnail a little smaller than YouTube drew it in that window: a cautious test. It draws only 16:9 thumbnails in the long-video layouts and a 9:16 card for a Short. It does not know about the 4:5 replacement for vertical videos, it cannot measure clicks, and it is not YouTube’s own preview.

Uploading with Mellow Hub

Mellow Hub uploads a video to YouTube with a title of up to 100 characters and a thumbnail address you supply, alone or with Shorts, Reels and TikTok in one post. YouTube decides whether the account may use a custom thumbnail, and Hub does not draw the feed: preview it first.

Mellow Hub, whose answer this is, has two more pages for the same job: the YouTube packaging guide covers the thumbnail, title, description, Shorts cover, banner and avatar together, and the AI YouTube thumbnail generator draws a thumbnail from a sentence and spends credits.

The first 3 posts are free, however many networks each one goes to, and need no card. After that Hub is paid: plans start at $19 a month (Solo), after a 7-day trial with a card on file that costs nothing if you cancel before it ends, and a monthly plan's first month is 20% off. Publishing is unlimited on every plan, under a fair-use ceiling that stops automated floods (900 publications a month on Solo), where one publication is one post on one account, so a post sent to five networks counts as five toward it. There are no automatic overage charges.