Slide Legibility Checker
Test whether the smallest text on a projected slide will subtend enough visual angle for the furthest viewer. The result is one measurable number: arcminutes.
No account. Nothing stored. Trigonometry only — no AI model call.
Describe the room and slide
Use the smallest important text on the slide, the image height on the wall, and the distance to the furthest viewer.
PowerPoint slide size, font size, and why only one of them matters
The most common fix people reach for is the wrong one. Here is what the slide dimensions actually do to readability.
| Setting | What it is | Effect on legibility |
|---|---|---|
| PowerPoint slide size (16:9) | Widescreen is 13.333 × 7.5 inches — 960 × 540 points, the design height this calculator assumes. | None on its own. The projector scales the whole slide to fill the wall, so text keeps the same proportion of the image. |
| PowerPoint slide size (4:3) | Standard is 10 × 7.5 inches — 720 × 540 points, the same 540-point height. | None on its own, for the same reason. Switching slide dimensions reflows your layout; it does not make 12pt text readable. |
| Font size in points | The height of the type relative to that 540-point canvas. | This is the lever. Doubling the point size doubles the visual angle at a fixed distance. |
| Projected image height | How tall the slide lands on the wall, in metres. | Directly proportional. A 1.2m image and a 2.4m image differ by a factor of two for identical slides. |
| Distance to the back row | How far the furthest viewer sits. | Inversely proportional. Twice as far back halves the visual angle. |
In other words: changing PowerPoint slide dimensions preserves legibility only when the content scales proportionally. If the calculator above says your text falls short, raise the point size, project a bigger image, or move the back row forward — those are the three variables in the arithmetic.
Slide design, PowerPoint slide dimensions, and legibility questions
What font size should slides be?
There is no single number, because it depends on the room. A 24pt body line reads comfortably in a small meeting room and can fail from the back of a lecture hall with the same deck. Rather than memorising a rule of thumb, run your smallest important text through the calculator with your real projection height and back-row distance — it returns the minimum point size for the 16-arcminute target.
What is the standard PowerPoint slide size?
Widescreen 16:9 is 13.333 by 7.5 inches, which is 960 by 540 points; the older 4:3 standard is 10 by 7.5 inches, or 720 by 540 points. Both share a 540-point design height, which is the figure this checker uses to convert your font size into a projected letter height.
Does changing the slide size make my text more readable?
Changing canvas size preserves legibility only if the text and other content scale proportionally, keeping text the same fraction of the projected image. This calculator assumes a 540-point design height; adjust the font-size input for other canvas heights. Slide design choices that genuinely help are fewer words per slide, a larger minimum point size, and enough contrast between the text and its background.
Check the whole deck before delivery
The calculator stays free. Gixo Lumen builds and exports editable decks with consistent layouts and reusable themes.
Standards behind this check: document accessibility standards, guides and testing tools.
Updated