“Usable” is the correct spelling that is more commonly used. “Useable” is a correct variant spelling but is used less often. Both words are acceptable in any English-speaking country, and they’re both used to mean that someone is able to use something.

“Usable” without the extra “e” is the preferred way to spell the word in American English. The addition of the “e” in “useable” is considered more common in British English and Europe.

In terms of American English, “usable” is the most acceptable version. Internationally, both “usable” and “useable” are acceptable spellings of the word. Most dictionaries list “useable” as a variant spelling.

Useable suggests an object's practicality and convenience for a certain purpose, hinting at ease of use or suitability for a specific task. Usable, on the other hand, emphasizes the capability of an object to be used, regardless of how convenient or practical it might be.

"Usable" is preferred in American English and is more likely to be found in formal writing, reflecting its status as the standard spelling. "Useable," on the other hand, might appear more frequently in British English, although "usable" is still the dominant form.