There is no single correct way to express likelihood or consequence tables. Each organization needs to consider their context and develop specific tables or metrics to suit their situation.
With that caveat, the following articles offers two examples of how such tables might be established. Your organization may choose to use only one, or perhaps various ways to group likelihood and consequence.
In the following examples, there are four categories for Likelihood and six categories for Consequences. Use the minimum number necessary to achieve your goal.
Guidance note: when using such tables choose:
The most statistically likely, or at least most credible likelihood for an event occurring
The range of potential consequences which you are 90% confident that the consequences will fall between, e.g. in the range of 3 to 5 (Moderate to Significant). The more precise the better but if you do not have solid evidence, this approach will at least allow you to express your level of uncertainty. This will help identify the level and type of information required in order to improve your predictions.
The following is one example of how likelihood tables can be structured
Consequence tables need to be customized for each specific organization or context. The following is just one example.