When someone asks a professional to create custom signs or banners, they may also wonder what size the products should be. It's important to strike a balance between big enough to do the job without getting ridiculous with the size. What determines that balance, though?
You'll want to take some time to determine how far your median viewer will be from the banner or sign. Roughly speaking, you'll need to have one inch of letter height for every ten feet the viewer will be away to achieve readability.
Factor in at least half of the letter to calculate vertical spacing if you're going to use two or more rows of text. If you have two rows of 6-inch text, for example, that will give you 12 inches of lettering. Add 50% of 12 inches to get 18 inches as the minimum height. You will probably also want to add a couple more inches of space around the letters to let the text breathe a bit.
Bear in mind, there are limits to what some products can do. Vinyl banners, for example, aren't stiff and will perform poorly in high-wind, outdoor spaces in large applications. Eventually, you will need to move up to a solid sign for a large project.
If you add imagery to a banner or sign, especially one that also has text, you don't want a busy mess. That means providing some room for the elements to operate independently. Such designs are often ideal for wider banners because you can put the imagery to one side and the text to the other.
Generally, highly stylized letters are harder for people to read. If you're using a script font, for example, you should consider increasing the size of the lettering anywhere from 50% to 100% to account for potential reading difficulties. Especially if the letters have long vertical flourishes, you may need more spacing between lines of text, too.
Much like imagery, complex colors tend to slow down reading and require bigger text. Typically, the best solution is to dial down the color scheme and avoid going bigger. However, if the colors are necessary, you should treat them similarly to stylized text and add significant size and space.
Light hitting a sign or banner can produce similar problems in terms of readability. Once more, increasing the size by at least 50% will reduce these issues.