There are formal Manuka honey grading systems in place to help consumers feel confident they're getting the real deal. The higher the number or rating for any of these, the more powerful the honey.
The most common grading system, which some consider the gold-standard, is the Unique Manuka Honey Factor (UMF). It was developed by the UMF Honey Association in New Zealand, and it grades Manuka honey based on its levels of MGO, DHA, non-peroxide activity (NPA), and leptosperin. Every jar of Manuka honey is given a rating from UMF 5+ to UMF 20+. Opt for honey with a UMF rating of at least 10+ to ensure it has sufficient potency to deliver real benefits.
The MGO grading system, which was developed by a New Zealand professor, measures only levels of MGO. Seek out Manuka honey with an MGO rating of 250 or higher, which is an approximately equivalent to UMF 10+.
The K-Factor rating system is used only by the brand Wedderspoon, but it's been given the OK by the New Zealand government. It measures markers such as purity, live enzymes, DHA, pollen count, pH levels, antioxidant levels, and phenolic compounds. Wedderspoon offers honeys with a K-Factor of 12 or 16, with K-Factor 16 containing more beneficial compounds.
Additionally, all Manuka honey is (by definition) raw and unpasteurized to preserve its beneficial live enzymes and other compounds. If you purchase Manuka honey featuring any of the above ratings, you can be sure it is raw and unpasteurized.