In determining likelihood of confusion, courts evaluate several factors. No one factor is determinative in and of itself, and how important one factor is over another is very case specific.  There are also differences in how each jurisdiction applies the likelihood of confusion test.  Below is a list of the main factors considered by most jurisdicitons in the United States.

Likelihood of Confusion Factors  

• Factor 1: Strength of the plaintiff’s mark. The greater the public recognition of a mark as a source identifier, the more likely that similar uses will be confusing.  This generally means the mark is not descriptive of the product, and is not frequently used (or diluted).  

• Factor 2: Similarities between the marks.  Similarity (in appearance, sound, or meaning) matters significantly; however, even identical marks may not be "confusingly similar," if the other factors weigh against finding consumer confusion.

• Factor 3: Proximity in channels of trade and marketing of the products on which the marks are used. If the respective products share distributors or can be found in the same stores, that weighs in favor of finding confusion.

• Factor 4: Likelihood that the plaintiff will expand its mark into defendant’s line of business (”bridging the gap”).  This captures the reasonable expectation that a consumer would believe the same company would sell their products in both areas (e.g. a seller of baby clothes would be expeccted to sell maternaty outfits as well).  Further, the more extensively used and the more popular the mark, the more likely it is that consumers will expect an expansion of the product base. 

• Factor 5: Defendant’s intent in adopting the mark. Likelihood of confusion does not require intent.  However, where a party deliberately sets out to adopt a similar trademark as that of a prior user's, it is reasonable to assume that the party knew enough of what they were doing to succeed in creating customer confusion.  

• Factor 6: Product relatedness.  

• Factor 7: Consumer traits (sophistication and care).  How careful the consumer is likely to be prior to purchasing. The more sophisticated the consumer (e.g. business owners versus children), or the more expensive the product, then the more discriminating the consumer is expected to be, and the less likely confusion will be attributed to them).

• Factor 8: Whether there has been any actual confusion. Even with actual confusion, the other factors must still be weighed, because actual confusion is not conclusive evidence of likelihood of confusion.
   

These factors grew out of the now-famous case, Polaroid Corp. v. Polarad Elect. Corp., 287 F.2d 492 (2nd Cir. 1961), and are sometimes referred to as the Polaroid Test.