Every reading app ships with defaults, and defaults are a guess about an average reader who does not exist. Someone decided what size the text should be, how far apart the lines should sit, and how wide the page should run — for everyone at once. The odds that their guess matches your eyes, your phone, your lighting and your hands are not good.
The fix takes about four minutes, once, and it changes how long you can comfortably read in a sitting. Here is the order to do it in, because some of these settings affect each other.
Change one thing, read two paragraphs, decide. Changing five settings at once tells you nothing about which one helped.
1. Line length first, not font size
This is the setting almost nobody touches and the one that matters most. Typographers have long aimed for somewhere in the region of fifty to seventy-five characters per line in body text, and the reason is mechanical: your eye has to travel back to the start of the next line, and a long line makes that return jump easy to get wrong. You end up re-reading the same sentence without knowing why.
On a phone held upright, you are rarely in danger of lines being too long. On a tablet, or a phone in landscape, you absolutely are. If your app offers margins or page width, widen the margins until a line is roughly eight to twelve words. If it does not, and you are reading on something wide, a smaller font is not the answer — a narrower column is.
2. Then font size, by a specific test
Hold the device where you actually hold it, not closer. Read one paragraph at normal speed. If you leaned in, squinted, or moved the phone, the text is too small. If your eyes are doing a lot of horizontal work to get through a short sentence, it is too big.
Most people set text slightly smaller than is comfortable, because a bigger font feels childish and means more page turns. Neither of those is a real cost. Page turns are free. Eye fatigue is not.
3. Line spacing, the cheap upgrade
If your app lets you increase the space between lines even slightly, do it. Tight line spacing makes a page look dense and makes that return-jump problem worse, because the line above and below are both crowding the one you are on. A small increase here often does more for comfort than two steps of font size — and it is the first thing to try if text feels heavy without being small.
4. Theme: match the room, not the hour
The dark-mode debate is usually argued as if one answer is correct. It is not. Dark text on a light background is generally easier to read in a bright room; light text on a dark background is easier in a dim one. The variable is the room, not the time of day, and the right habit is switching rather than committing.
A sepia or warm off-white theme is worth trying even if you think you are a pure black-and-white person. Lower contrast than pure white, less stark than full dark, and for many people the most comfortable option for a long session. Cycle through all three over a week before you decide.
5. Brightness lower than feels right
Set brightness so the screen roughly matches the brightness of the wall or page beside it. Most screens are set far above their surroundings, which is fine for ten seconds of messages and tiring across an hour of prose. Turn auto-brightness on if you move between rooms; turn it off if it keeps changing mid-paragraph and pulling your attention off the sentence.
6. The settings that are not about comfort
Two more worth finding. Serif or sans-serif is largely preference — try the one you do not normally use for a chapter, since familiarity is doing more work here than legibility. Justified text looks tidy but can open ugly gaps between words on a narrow column; left-aligned is usually the safer choice on a phone.
And if you find yourself re-reading the same page, the problem may not be visual at all. Interruptions break reading far more effectively than a bad font does, which is a separate job covered in how to read on your phone without distractions.
Accessibility settings are reading settings
If small text is genuinely hard work, your phone's system-wide text size and bold-text options exist, and using them is not a compromise. Text-to-speech is also a legitimate way to read a book rather than a lesser one — we make that case in listening to books with text-to-speech, and switching between reading and listening in the same book is one of the real advantages of reading on a phone.
Readers who find sustained attention difficult often get more from spacing, shorter sessions and audio than from any font change; there is more on that approach in how to read with ADHD.
Do it once, then stop fiddling
There is a failure mode here: tuning the app becomes the activity. Give yourself one session of adjusting, write down what you landed on, and then leave it alone for a month. Settings are supposed to disappear.
In Arwy, our Android reading and writing app, these controls live together in the reader — theme, font, size, alignment, plus text-to-speech and offline reading — and whatever you choose is remembered across books, so you set it up once. To be straightforward about the limits: there is no iOS version, so if you read on an iPhone this particular app is not an option for you, and if you mostly read paper, none of this applies — a decent lamp will do more than any setting.
Set it up once, then read. Arwy is on Google Play.