Teleprompter / Free tools / Text size calculator
Text size calculator
Enter how far you stand from the screen, which screen it is and whether it sits under glass. You get a starting text size, how many words fit a line, and how far your eyes move as you read.
On this page
The formula, and its assumption
The assumption. A capital letter should fill about half a degree of your view. That is a little larger than the print in a book held at reading distance, so a line reads at a glance rather than with effort. It is a starting point: eyesight, light and the face you choose all change it, so check from your mark and adjust.
The steps.
- Viewing distance. Your distance to the screen. Behind glass you see the screen reflected, so it is your distance to the glass plus the screen's distance below it.
- Letter height. Capital height = 2 × distance × tan(0.25°), which is about 8.7 mm for every meter.
- Type size. A capital letter is about 0.7 of the type size, so type size = capital height ÷ 0.7.
- Points on the device. The app's Text size is in points, and iPhone, iPad and Mac screens each show a set number of points per inch (about 153 on an iPhone, 132 on an iPad and 127 to 129 on a MacBook at the standard setting).
- Words a line. The screen's width, less the margins, divided by an average character of half the type size, and six characters to an English word with its space.
- Eye movement. The angle a line takes up from where you stand, and, without glass, the angle between the reading line and the lens.
Starting sizes by distance
| Distance | Capital height | iPhone, under glass | iPad 11 inch, under glass | MacBook 16 inch, no glass |
|---|---|---|---|---|
| 0.5 m (1.6 ft) | 4.4 mm | 49 pt | 42 pt | 31 pt |
| 1 m (3.3 ft) | 8.7 mm | 86 pt | 75 pt | 62 pt |
| 1.5 m (4.9 ft) | 13.1 mm | 124 pt | 107 pt | 94 pt |
| 2 m (6.6 ft) | 17.5 mm | 161 pt (over 160) | 139 pt | 125 pt |
| 3 m (9.8 ft) | 26.2 mm | 237 pt (over 160) | 204 pt (over 160) | 187 pt (over 160) |
The app's Text size runs from 18 to 160 pt. A result over 160 means the screen is too small for that distance: move closer, or use a bigger screen such as a display wired to the device as a clean feed.
What to do with the numbers
- Too few words a line? Below about three words, the scroll has to move fast and reading gets choppy. Narrow the margins or use a bigger screen.
- Eyes moving a lot across a line? Widen the margins to shorten the line, or stand further back. Behind glass, the further the camera, the smaller the movement.
- Eyes far off the lens? Without glass, move the words closer to the lens or step back. On iPhone and iPad, Cutvey Teleprompter's recording mode puts the script in a strip right beside the lens. On a Mac call, Call mode parks it under the camera. Behind glass the words sit over the lens.
In Cutvey Teleprompter: the Text page sets the size (18 to 160 pt) and the margins (0 to 40 percent); Reading line & screen moves the reading line from 20 to 80 percent of the way down. Fonts and reading aids · Rig setup.
What it keeps and sends
Nothing. Every number is worked out in this page, nothing is stored and nothing is sent.
Reading for real? The app does the rest.
Cutvey Teleprompter sizes the text from 18 to 160 pt, sets the margins and the reading line where you want them, mirrors for glass and sends a clean feed to a bigger display. $19.99 once for iPhone, iPad and Mac.