In order to easily rate wines, I always use the 100 point scale. Wines get rated a score between 1-100, but actually it should be called the 50-100 scale, as everything below 50 points will be almost undrinkable!
The different scores explained:

50-59 Wine contains many flaws and should only be used for cooking. 

60-69 The wine still contains a lot of flaws, but is drinkable. These are wines made in bulk from the supermarket, without mentioning a winery or a determination of origin.

70-79 These are the wines that have less flaws and have a specific winery and vintage mentioned on the label. Yet the wines still taste rather ordinary and are produced in bulk. This is mostly for the typical ‘house blends’ of restaurants.

80-84 The determination of origin becomes more clear and specific, also the vintage becomes more important. These wines are classified as above average to good.

85-90 Wines become more complex, and the aftertaste is longer. These wines are classified as good to very good.

91-94 The complexity rises, and the determination of origin will usually contain the mentioning of a specific village or vineyard. The quality of these wines is very good up to excellent.

95-100 These are usually wines from a specific soil, vintage or vineyard. Wines with this score belong to the absolute top!