Typography Mistakes That Make Slides Hard to Read, and How to Fix Them

Sit at the back of any conference room during a presentation and watch what happens when a dense slide comes up. People squint. A few lean sideways to see past a head. Someone gives up and checks their phone. The speaker says “as you can see here,” and almost nobody can.

Most unreadable slides aren’t badly designed in the sense of being ugly. Plenty of them look fine on a laptop screen at arm’s length. They fail at distance, on a projector with washed-out contrast, or on a video call where the deck has been shrunk to a quarter of someone’s monitor. Typography decides most of that, and a handful of mistakes account for most of the damage.

Mistake 1: Body text that’s too small

Designers who are used to print or web work bring those sizes into slides, and 12pt or 14pt body copy looks perfectly reasonable in the editing view. On a projected screen 8 metres away, it doesn’t.

A rough working rule: body text at 24pt or larger for presentations given in a room, and nothing below 18pt anywhere on the slide, including footnotes and chart labels. Titles at 36pt and up. If your content doesn’t fit at those sizes, there’s too much content on the slide, and the fix is to split or cut it, not to shrink the type.

A quick test that I still use: put the slide on your laptop, step back about three metres, and try to read it. If you can’t, the back row won’t either.

Mistake 2: Thin weights and light styles

Font families like Montserrat, Poppins and Raleway ship with beautiful Thin and Extra Light weights. Those weights look elegant on a large hero banner on a high-resolution screen. On a projector, especially an older one in a bright room, the strokes disappear. Text set in Raleway Thin at 20pt can fade to almost nothing.

For body copy on slides, stay at Regular (400) or above. Medium (500) often reads better than Regular on projectors because the slightly heavier stroke survives the loss of contrast. Save Light weights for very large display text, and even then check them on the actual screen if you can.

Mistake 3: Decorative fonts for body text

Script faces, heavily stylised display fonts, and anything with ornate swashes have their place: a single word on a title slide for an event, a wedding slideshow, a poster-style opener. They fall apart as paragraph text. Pacifico, Lobster or Great Vibes are lovely in the right context, and a bullet list set in any of them is hard work for an audience.

The usual approach is a pairing: an expressive display face for titles and a clean, sturdy text face for everything else. Some pairings built entirely from free fonts that hold up well on screen:

Titles	Body	Feel
Playfair Display	Source Sans 3	Editorial, classic
Space Grotesk	Inter	Technical, modern
Bebas Neue	Open Sans	Bold, punchy
DM Serif Display	DM Sans	Warm, polished
Archivo Black	Archivo	Strong, single-family

Bebas Neue is all-caps by design, which makes it good for short titles and poor for anything longer than a few words. Keep that in mind before setting a two-line headline in it.

Mistake 4: Too many fonts

Three typefaces on one slide is usually one too many. Five is chaos. This tends to happen gradually: a template uses one font, somebody pastes a chart from Excel that brings in Calibri, another person copies a quote from a web page and it arrives in Arial, and by the final version the deck has six fonts nobody chose.

Two families is plenty for most decks. One family with a good range of weights (Inter, IBM Plex Sans, Roboto, Source Sans 3) can carry an entire presentation on its own. Before a final review, check the font list in your presentation software and replace anything you didn’t pick deliberately.

Decks that start life in an ai presentation maker usually begin with a single theme applied across every slide, so the font list is short at first. The stray families come in later, through pasted charts and copied quotes, which is why the check belongs at the end of editing rather than the start.

Mistake 5: All caps for long text

Uppercase works for short labels and titles. For sentences, it slows reading noticeably, because word shapes become uniform rectangles and readers lose the cues that ascenders and descenders give them. A slide with three bullet points in capitals reads like someone shouting a contract at you.

If you want the visual weight of caps for a section label, use it on two or three words and add a little letter spacing (around 5 to 10 percent of the font size, depending on the typeface). Leave the sentences in sentence case.

Mistake 6: Poor contrast

Light grey text on white. Dark blue on black. Pale yellow on a photograph of a beach. These combinations look subtle and sophisticated on a calibrated design monitor and turn invisible on a conference room projector.

Aim for strong contrast between text and background, and if you want something to check against, the WCAG accessibility guidelines suggest a contrast ratio of at least 4.5:1 for normal text and 3:1 for large text. Many free contrast checker tools will calculate the ratio for any two colours. Text over photographs needs special care: either place it on a solid or semi-transparent band, or choose a part of the image that’s uniformly dark or light.

Mistake 7: Long lines and cramped spacing

A text box stretched across a whole 16:9 slide gives you lines of 100 characters or more. The eye loses its place jumping back to the start of the next line. Narrow the text box so lines run somewhere around 50 to 75 characters, and use the remaining space for an image or simply leave it empty.

Line spacing matters too. The defaults in most presentation software are fine for a single line and tight for a paragraph. Bumping line spacing to around 1.2 to 1.4 times the font size, and adding a little space after each bullet, makes even a dense slide feel calmer.

Mistake 8: Centre-aligned paragraphs

Centring a title is normal. Centring a five-line paragraph or a bulleted list makes every line start in a different place, so the reader has to hunt for each beginning. Left-align body text and bullets. Centre short headings, single quotes, and the occasional standalone number if it suits the layout.

Mistake 9: Ignoring how fonts travel

You build the deck with a lovely free font installed on your machine, send it to a colleague, and their copy falls back to Calibri or Times New Roman. Line breaks shift, text overflows boxes, a title wraps onto three lines.

There are a few ways around this. Use fonts available in the platform you’re presenting from (Google Slides has a large library of Google Fonts built in, for instance). Embed fonts where your software allows it. Or export a PDF for anything that needs to look exactly right on someone else’s machine. If you’re presenting from a conference laptop, carry both the editable file and a PDF.

Mistake 10: Chart labels nobody can read

Charts get pasted into slides straight from spreadsheets, and spreadsheet defaults are designed for a screen you sit 50 centimetres from. Axis labels at 9pt, a legend in 8pt, data labels crammed onto every bar. On a projector, the chart becomes a coloured shape with grey specks around it.

Rebuild or restyle the chart inside the presentation instead of pasting a picture of it. Set axis labels and legends to at least 16 to 18pt, in the same body font as the rest of the deck. Remove gridlines you don’t need. Label the two or three values you’ll actually talk about directly on the chart and drop the rest. If the chart still feels crowded, put the full version in an appendix or a handout and show a simplified one on the slide.

Where AI tools fit in

A lot of slide drafts now start in an AI tool, where you paste in notes or a prompt and get back an outline and designed slides you can edit. That’s a real time saver for structure and first-pass layout. The typography in those drafts is usually sensible by default (readable sizes, a limited set of fonts), but it’s still a draft, and the same mistakes can creep in once you start adding your own content.

The common pattern I see goes like this. The tool generates a clean slide with a title and three short bullets. Then the author pastes in a full paragraph from a report, the text box auto-shrinks the font to make it fit, and suddenly the body copy is 13pt. The tool did its job. The edit undid it.

When you take an AI-generated deck into editing, check these things:

Turn off auto-fit or “shrink text on overflow.” Most presentation software has this setting. It hides the problem by shrinking type instead of telling you to cut.
Check the font list. If you pasted anything from elsewhere, there may be stray fonts in the file.
Apply your own pairing if the defaults don’t suit your brand. Change it in the theme or master slide, not slide by slide.
Look at contrast on any slide with a background image.

You can also ask for typography choices directly in your prompt. Something like this tends to produce a cleaner starting point:

Make an 8-slide presentation for a design studio’s client workshop on brand refresh options. Keep each slide to a title and no more than three short bullets. Use a serif display font for titles and a clean sans-serif for body text. Dark text on light backgrounds. No slide should need text smaller than 20pt.

The tool won’t always follow every instruction perfectly, but it gives you a closer starting point than a generic request, and you’ll spend less time fixing type afterward.

Before and after: one slide

Here’s a slide from a typical internal deck, described rather than shown:

Before: Title in Raleway Light, 28pt, pale grey. Body is a seven-line paragraph in Raleway Light, 14pt, centred, running the full width of the slide. A stock photo of an office behind everything at full opacity. A footnote in 9pt.

After: – Title in Raleway SemiBold, 40pt, near-black, left-aligned – Paragraph cut to three bullets, Source Sans 3 Regular, 24pt, left-aligned in a text box about 60 percent of the slide’s width – Photo moved to the right third of the slide, with the text sitting on a plain off-white background – Footnote moved to the speaker notes

Same message, same branding colours. The second version can be read from the back of the room, and the first one couldn’t (it barely survives a laptop screen). Small typographic changes compound; none of these edits took more than a minute, and together they change how the slide lands.

A short checklist for your next deck

Before you present, click through every slide in presentation mode and look for:

Any text under 18pt
Any weight lighter than Regular in body copy
More than two font families
Sentences in all caps
Text over busy images without a backing panel
Lines that run edge to edge across the slide
Centred paragraphs or bullet lists
Fonts that might not exist on the presenting machine

If you’re working from an ai presentation maker draft, run this check after your edits, not before. Most typography problems arrive in the editing stage, when real content meets a tidy template.

Common questions

Is serif or sans-serif better for slides? Both can work. Sans-serifs with open shapes and generous x-heights (Inter, Open Sans, Source Sans 3) are a safe default for body text on screens. Serifs like Merriweather or Lora read well at large sizes and add character to titles.

Can I use a free font in a client presentation? Usually yes, but check the licence. Most fonts on Google Fonts are released under the SIL Open Font License, which permits commercial use. Other free fonts may restrict commercial work, so read the licence file that came with the download.

What about variable fonts? They’re handy for fine-tuning weight, and many presentation tools now handle them, though support varies. If in doubt, use the static weights and test on the presenting machine.

One habit to keep

Print a slide. Just one, at actual size on a sheet of A4 or letter paper, and pin it to a wall on the far side of a room. Walk away until you can’t read it. That distance, roughly, is where your audience’s last row is sitting, and it tends to make the case for bigger, bolder, simpler type better than any rule ever could.