Image size requirements will vary based on your needs. A general rule of thumb follows, however, we always recommend you consult with the printer of your work for their specific requirements.
Small - images used on websites or web design
Medium - small print jobs, such as brochures, flyers and business cards
Large - prints, full page ads, large book covers
XL - very large prints, posters, trade show signage, billboards
Vectors - can be scaled to any size, using vector editing software, such as Adobe Illustrator, without loss of quality and are ideal for very large signage, vehicle wraps, etc.