Reference
Social media caption length limits
Caption limits for a standard account are about 280 characters on X, 300 on Bluesky, 500 on Threads, 2,200 on Instagram, 3,000 on LinkedIn, 4,000 on TikTok and 63,206 on Facebook. Feeds show far less before a "more" link, so put the point in the first line.
Limits change
Networks raise and lower limits, and paid accounts sometimes get more. Check the network's help page before planning a long post.
The first line does the work
Instagram shows roughly the first 125 characters and LinkedIn roughly the first 210 before cutting off. Write that first line as if it is the whole post.
Links and emoji count differently
X counts any link as 23 characters. Some emoji take more than one character slot. A checker that counts like the network saves a failed post.
Quick answers
How many hashtags can Instagram take?
Up to 30 in a caption.
Does a longer caption do better?
Not on its own. A clear first line matters more than length.