Strictly, the 78k is for subscribers (probably meaning people who get the emails), not readers; someone who uses RSS to keep up or just visits the site every now and then won’t be counted. I don’t have much intuition for how many readers will be subscribers.
ACX is probably a better reference class: https://astralcodexten.substack.com/p/2023-subscription-drive-free-unlocked. In Jan, ACX had 78.2k readers, of which 6.0k subscribers for a 7.7% subscription rate.
Strictly, the 78k is for subscribers (probably meaning people who get the emails), not readers; someone who uses RSS to keep up or just visits the site every now and then won’t be counted. I don’t have much intuition for how many readers will be subscribers.