Note, the Endocrine Society currently suggests a minimum 25(OH)D level of 30 ng/ml (75 nmol/liter) and suggests much higher levels of supplementation if you need to raise it: "to raise the blood level of 25(OH)D above 30 ng/ml may require at least 1500 –2000 IU/d of supplemental vitamin D."
Holick, Michael F., Neil C. Binkley, Heike A. Bischoff-Ferrari, Catherine M. Gordon, David A. Hanley, Robert P. Heaney, M. Hassan Murad, and Connie M. Weaver. “Evaluation, Treatment, and Prevention of Vitamin D Deficiency: An Endocrine Society Clinical Practice Guideline.” The Journal of Clinical Endocrinology & Metabolism 96, no. 7 (July 1, 2011): 1911–30. https://doi.org/10.1210/jc.2011-0385.
It's also worth noting that studies have shown that without sun exposure, people may require even higher levels of supplementation to maintain their 25(OH)D levels:
Heaney, Robert P., K. Michael Davies, Tai C. Chen, Michael F. Holick, and M. Janet Barger-Lux. “Human Serum 25-Hydroxycholecalciferol Response to Extended Oral Dosing with Cholecalciferol.” The American Journal of Clinical Nutrition 77, no. 1 (January 2003): 204–10. https://doi.org/10.1093/ajcn/77.1.204.
"CONCLUSIONS: Healthy men seem to use 3000-5000 IU cholecalciferol/d, apparently meeting > 80% of their winter cholecalciferol need with cutaneously synthesized accumulations from solar sources during the preceding summer months. Current recommended vitamin D inputs are inadequate to maintain serum 25-hydroxycholecalciferol concentration in the absence of substantial cutaneous production of vitamin D."