Choose 1920×1080 for a Roblox thumbnail
Start your Roblox thumbnail at 1920×1080 when creating a new design. This canvas matches the recommended dimensions without enlarging smaller finished artwork. Both 1920×1080 and 1280×720 have a 16:9 aspect ratio: the width is about 1.78 times the height. The difference is the number of pixels available to describe the same scene.
A 1280×720 thumbnail contains about 0.92 million pixels, compared with 2.07 million at 1920×1080. If 720p is your only source, this tool can enlarge it to the target size, but inspect small lettering and character edges afterward. Keep the original file so you can replace it with a sharper capture later.