Speech Bubble Sizing Calculator

Fill ratio represents how much of a shape's bounding box the text block can actually occupy given the shape's geometry. A caption box (a plain rectangle) reaches 90% because there's almost no wasted corner space, a rectangle bubble uses 85%, an ellipse drops to 64% because its curved edges cut into the corners where text would otherwise sit, and a thought-cloud falls to 55% because its scalloped, bumpy outline wastes even more edge space than a smooth ellipse.

The calculator assumes 5.5 characters per word for all-caps lettering (the comics standard) versus 5.2 for mixed case, on the reasoning that mixed-case text runs slightly more compact than uppercase-only lettering. That's a small per-word difference, but it compounds across your full word count when computing total characters, so a long line of dialogue in mixed case comes out modestly narrower or shorter than the same dialogue in all caps.

Panel Coverage compares the calculated bubble's area to the total panel area, and the calculator's guidance is to keep it under roughly 25% — beyond that, a bubble starts visually overwhelming the artwork rather than sitting comfortably within the panel. If your coverage percentage comes back high, the fix is usually a smaller font size, fewer words, or a larger panel, since the bubble dimensions themselves are just a function of those three inputs.

It's a simple three-tier heuristic, not a continuous formula: a score of 100 requires both a word count between 5 and 35 and 3 to 8 words per line. A score of 40 applies if word count exceeds 50 or words per line drops below 2 (both signs of cramped, hard-to-parse lettering), and everything else in between scores 70. It only looks at word count and words-per-line — font size and bubble shape don't directly affect the score.