This varies according to age and gender. It is recommended:
Infants and children up to 4 years of age: 20 mg per day
Children 13-15 years old: 85 mg per day
15-19 years old
Male: 105 mg per day / Female: 90 mg per day
Adult:
Male: 110 mg per day / Female: 95 mg per day
Pregnant female: 105 mg per day
Breastfeeding female: 125 mg per day
Smokers (have higher metabolic losses and lower vitamin C concentration in the blood than non-smokers!!)
Male smokers: 155 mg per day / Female smokers: 135 mg per day
Information provided by Deutschen Gesellschaft für Ernährung e.V (the German Nutrition Society)