There's no single required banner size. The right size depends on where the image goes and which template your event uses.

Standard form banner (Main Image)

The Main Image is set under Plan > Configure > Display > Extended Display, in Images and Attributes. You pick it from the images uploaded to the event's Assets. The form is 800 pixels wide by default. A wider banner makes the page wider, up to 2500 pixels wide and 300 pixels tall. See Recommended Dimensions for Extended Display > Main Image Field

Power Template and PRO Template banners

These banners go in the content file's banner section, with a separate image for each screen size. The recommended sizes are:

• Desktop: 1920 x 750 pixels
• Tablet: 1200 x 675 pixels
• Mobile: 650 x 1000 pixels

The same sizes are listed in the header row of the banner file. If your template was customized, these sizes may not fit. Check with whoever built it. See Power Template: update the content file, and fix sections that aren't showing

Your own template

If you built your own template, the right size depends on how it was designed. Make the image at least as wide as the banner area so it doesn't get stretched.

Common problems

• Blurry banner: the image is smaller than the banner area, so it gets stretched. Upload a larger image.
• Image shows as text or code: paste only the file path in the field, with no HTML tags, and remove spaces from the file name.
• Upload fails: the file is too large. The default upload limit is 4 MB. An Administrator can raise it to 25 MB by turning on Increased file upload limit under Plan > Configure > Options. Otherwise, make the file smaller.
  
• Top or sides cut off: banners are resized to fit each screen. Keep text and logos away from the edges.

Next step: Check where your banner goes, then upload an image at least as wide as that area.