One summer, when I was feeding an ounce of salt a day and had a 7 lb Redmond block, I calculated my horse was going through a pound of salt a week.
Right now she has a 50 lb block I gave her in October 2021, which is quite worn after 14 months, and gets an ounce daily in her mash but that’s been inconsistent over the past year. I ran out in the summer and took a while to source plain white again.
But if you think about it, going through a 50 lb block in a year would be a pound a week. I don’t know how long most horses blocks last.