Good question! Google says:
How much vitamin D is in cod liver oil?
You're quite right that cod liver oil is a good source of vitamin D. According to the National Institutes of Health, it gives you 1,360 IU per tablespoon (I now recommend 2,000 IU daily).
Cod Liver Oil for Vitamin D? - Dr. Weil
https://www.drweil.com/vitamins-supplements-herbs/.../cod-liver-oil-for-vitamin-d/