There is a chart that breaks down the prestige ranges in the Workshop section of the EC Manual

From EC help
1.6.2 Production

The number of workshops you can use simultaneously depends on the prestige value of your equestrian center:

Between 0% and 20% prestige: 1 active workshop
Between 20% and 40% prestige: 2 active workshops
Between 40% and 60% prestige: 3 active workshops
Between 60% and 80% prestige: 4 active workshops
Between 80% and 100% prestige: 5 active workshops

Great thank you everyone!