How Many Characters Fit on a Button?
The maximum number of characters that fit on a button is calculated by taking the button width, subtracting horizontal padding to get the usable width, and dividing by the average width per character. Korean and Japanese (with kanji) characters are built from combined block-shaped forms, so each character's width is roughly equal to the font size and stays fairly consistent. English letters, by contrast, vary widely in width (compare 'i' and 'W'), averaging around 55% of the font size.
For example, a 160px-wide button with 32px total padding and a 16px font gives a usable width of 128px. At 16px per character for Korean, that's a maximum of 8 characters on one line. Since a wrapped or truncated label makes it harder for users to grasp meaning before clicking, keeping labels short and action-oriented is a core UX writing principle.
Actual results vary with letter spacing, kerning, and font weight, so it's safer to design with 1-2 characters of buffer below the calculated maximum.
Frequently Asked Questions
Wrapping or truncation makes meaning harder to grasp, hurting click-through and usability.
Korean characters have a consistent width; English letters vary widely and average narrower.
Yes, font properties vary — leave a 1-2 character buffer.