YouTube thumbnails: size, design and A/B tests

Custom YouTube thumbnails are uploaded from YouTube Studio if your account is verified, and YouTube's help recommends for videos a JPG or PNG image in 16:9, at a resolution of 3840x2160 pixels and a minimum width of 640 pixels. Beyond size, three things count: that it reads when small, that it complies with YouTube's policies and, if you have access, testing several versions with its A/B tests.

Thumbnail size and format

This is what YouTube's official page on custom thumbnails recommends:

Requirement	Videos	Shorts
Recommended resolution	3840x2160 pixels	2160x3840 pixels
Minimum	Width of 640 pixels	Height of 640 pixels
Aspect ratio	16:9	9:16
Format	JPG or PNG	JPG or PNG
Maximum file size	2 MB from mobile and 50 MB from a computer	50 MB from a computer

The thumbnail image should be as large as possible, because it is also used as the preview image in the embedded player. For Shorts, for now, custom thumbnails can only be added in YouTube Studio from a computer. And a warning for vertical videos: if you give them a 16:9 thumbnail, on the Home, Explore and Subscriptions pages it is replaced by an automatically generated 4:5 one.

How to upload a custom thumbnail

YouTube lets you choose one of the options it generates automatically or upload your own if your account has been verified (how to do it, in verifying a YouTube channel). From a computer:

1. Sign in to YouTube Studio and, in the left-hand menu, select Content.
2. Go to the video you want to edit.
3. Under “Thumbnail”, click Upload file to use an image from your device, or Get suggestions for YouTube to generate one.
4. Click Save.

Changes to thumbnails can take a while to show up on YouTube. And a channel can upload a limited number of custom thumbnails per day: if the “Daily custom thumbnail limit reached” error appears, YouTube says to try again after 24 hours. That limit can vary by region, country or the channel's history, and strikes affect it.

The thumbnail is one of the items on the checklist for publishing a video on YouTube; here it is in detail.

How to design it to be readable on mobile

Normally, people see the thumbnail and the title first, and decide from those whether to watch the video. YouTube's tips for creators on thumbnails are specific:

• If you add text, use a typeface that is easy to read.
• Try not to make the design too complex: a dynamic composition and colours make it more attractive, but overloading it can work against you.
• You can apply the rule of thirds and overlay your branding and some descriptive text.
• Thumbnails are displayed differently depending on the device, so make sure it is as large as possible.

And on your own, before uploading it:

• Few words, in large type. The title already tells the topic; the thumbnail does not need to repeat all of it.
• Look at it small. Shrink it to the size at which it appears in the mobile list. If you have to lean in to read it, there is too much text.
• Contrast. Light text over a dark area or the other way round, or with an outline if the background is uneven. How to choose colours that read well, in colour palette for a YouTube channel.
• Consistency. The same colours and the same typeface on all the channel's thumbnails, so they are recognised before the name is read.

For example, a history channel with a video titled “Why the steam train disappeared (and what was left of it)” could put just “THE LAST STEAM TRAIN” on the thumbnail, in thick white letters over the dark part of a photo of a locomotive.

AI thumbnails: what to know

YouTube Studio has its own AI help: according to its thumbnails page, Ask Studio analyses your video's transcript and topics to suggest thumbnails that suit it, and you can ask it for changes, such as increasing the size of the thumbnail's text.

If you generate the image with another tool, three precautions:

• Text, separately. If the model writes letters inside the image, check them one by one. It is safer to generate the image without text and add it afterwards with a typeface.
• The image must be in the video. A spectacular scene that then does not appear is exactly what the thumbnail policy does not allow: the thumbnail making people think they will see something that is not in the video.
• No faces or brands that are not yours. The thumbnail policy reminds you that YouTube does not allow unauthorised impersonation of a person, an entity or a channel that could mislead, and that this can include using AI to copy a person's voice or likeness so that it looks as if the channel is theirs or has their authorisation.

What a thumbnail cannot show

All custom thumbnail images must comply with the Community Guidelines. The thumbnail policy asks you not to publish any that shows, among other things:

• Pornographic images, sexual acts or nudity.
• Violent images intended to shock or disgust, or explicit or disturbing images with blood or mutilation.
• Vulgar or lewd language.
• Thumbnails that make users think they will see something that is not in the video.

The page itself makes clear that the list is not exhaustive. If a thumbnail breaks the rules, YouTube may reject it and your account may receive a strike; if the violations are repeated, it may remove your privileges to use custom thumbnails for 30 days or even terminate the account. And there is an in-between case: a thumbnail that does not break the rules but is not suitable for all users can end up with an age restriction on the video or its removal, with no strike for the channel.

Testing and comparing thumbnails: A/B tests

YouTube's help explains it in A/B testing for titles and thumbnails: creators can test and compare up to three different titles and thumbnails, and at the end of the test the option with the highest watch time is shown to all viewers. YouTube gives priority to total watch time over other metrics, such as click-through rate.

Requirements for using it:

• Only on a computer, through YouTube Studio.
• Advanced features must be enabled.
• It does not work for Shorts, scheduled live streams or premieres, although it does for archived live streams.
• It cannot be used on videos that are made for kids, age-restricted or private.

It is launched from the video itself: in the Title or Thumbnail box, click A/B Testing, choose Title only, Thumbnail only or Title and thumbnail, and upload up to three options. The test should complete within two weeks at most, and if you change the title or thumbnail while it is running, it stops automatically.

At the end you will see one of three results: “Winner”, “Performed same” or “Inconclusive”; in the last case, the title and thumbnail you uploaded first remain as the defaults. Two tips from the same page: test on older videos first, to reduce the impact on the channel's views, and run varied tests, because with options that are too similar the test may take longer than you would like to pick a winner. Watch the resolution: if any thumbnail in the experiment falls below 720p (1280x720), all of them are reduced to 480p (854x480). The results are in the Reach tab of Analytics; what to look at there, in YouTube metrics.

What the Estudio de Canales does with thumbnails

The Estudio de Canales composes three thumbnails per video and includes them in the package for uploading, as thumbnail-1.png, thumbnail-2.png and thumbnail-3.png. This is how it makes them:

• Over the video's visuals. The background comes from the scene images (the first three that have an image, or the ones you choose), cropped to 1280×720 pixels. If there is no image, the background is the accent colour.
• With the title text. By default, the title up to its first pause and at most six words, in capitals; you can write a different one of up to 60 characters, although at most three lines are drawn and whatever does not fit is left out. The studio writes the text itself with its own typeface, the same for all channels (not the one the bible specifies), rather than the image model, so that it comes out legible and free of spelling mistakes.
• Three compositions. Text on the left over a dark gradient, a bottom band in the accent colour, or large, centred text with an outline.
• The accent comes from the bible. It is the first in the list of colours in the channel's audiovisual style (how it is written, in the YouTube channel bible), provided it is written as a six-digit hexadecimal code, for example #1A6B5C; otherwise the studio uses its own default colour. That accent is only visible in the band of the second composition and, when there is no image, in the background.
• Measured contrast. In the first two, the text is white or black depending on the background behind it; in the third, white with a black outline. Contrast is calculated with the WCAG 2.1 formula.
• Small-size test. For each thumbnail, the height the lettering would have when seen at 168×94 pixels is calculated and, with the contrast, it is flagged whether it is legible. If none passes the legibility test, the “ready to publish” review warns you, without blocking.

What it does not do: it does not upload the thumbnails or launch A/B tests. You choose them and upload them yourself in YouTube Studio, and if you have access to the tests you can use all three. Nor does it make vertical thumbnails for Shorts. And its size, 1280×720, exceeds the minimum width of 640 pixels and does not fall below 720p, but is below the 3840x2160 resolution YouTube recommends: if you want more resolution, redo the one you choose from the same design.

Sources consulted

Checked on 11 October 2026. We link to the original source so that you can consult the current text.

• Añadir miniaturas personalizadas en YouTube. Google · Ayuda de YouTube.
• Consejos sobre miniaturas y títulos. Google · Ayuda de YouTube.
• Política sobre miniaturas. Google · Ayuda de YouTube.
• Pruebas A/B de títulos y miniaturas. Google · Ayuda de YouTube.