Role of Size in Logo Design
Like many other things, when it comes to logo design, size does matter. A logo has to look good and be legible at all sizes.
A logo is not effective if it loses too much definition when scaled down for letterheads, envelopes, and small promotional items. The logo also has to look good when used for larger formats, such as posters, billboards, and electronic formats such as TV and the Web.
The most reliable way to determine if a logo works at all sizes is to actually test it yourself.
Note that the smallest scale is usually the hardest to get right, so start by printing the logo on a letterhead or envelope and see if it is still legible.
You can also test for large-scale rendering by printing a poster-sized version at a print shop.