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What if you gave a presentation but nobody watched?

How would you feel about delivering a presentation to a blindfolded audience? Odds are that you wouldn't be a happy camper, not after all the time it took to develop your slides.

Your audience probably wouldn't be too pleased either, hearing you say things like "As you can see in this slide ..." when in fact they couldn't see anything at all.

Using hard-to-read or illegible visuals is like blindfolding your audience. It's also a lot like shooting yourself in the foot. The surprising thing is how often presenters handicap themselves, and their audiences, this way, considering how easy it is to do it right. Here's how you can avoid the pitfalls of illegibility and help your audience see the light.

Playing to the cheap seats

The key to legibility is making sure that your audience, even the folks waaaayy in the back row, can easily read the text on your visuals. As soon as they start to squint, you've started to lose them.

Make your text large enough for them to read and you've won half the battle. If your text is big enough, it will be readable.

But how big is "big enough?"

That depends on the particular situation. A complete answer would have to take into account the size of the room and screen, lighting
conditions, age of the audience and a host of other considerations. See below for a detailed explanation, but for now, the short answer is 8H.

The 8H Rule

The 8H Rule has long been used in the audiovisual industry to guarantee legible projected text. It says that the last row of seating should be
no further away from the screen than eight times the height of the screen (8H). Make your text at least 1/50th the height of the screen, and everybody in the room will be able to read your visuals.

If you're forced to use a room that's twice as long as the 8H rules says it should be, simply double your minimum text height. If you know you'll be working with a big screen in a small room, you can use smaller text. Like most rules of thumb, the 8H Rule is highly adaptable.

And like most rules of thumb, there are plenty of exceptions, caveats and "Yes, but"s. We'll get to those in a bit, but for now, the 8H Rule is a great starting point.

Caveat Projector

There are a few things about the 8H Rule you should keep in mind. First and foremost: the rule recommends minimum legible text heights, not ideal easy-to-read text heights. If you follow the rule, your text will be readable, but not necessarily easily, comfortably readable.

You can generally use minimum size text for chart axis labels, footnotes and the like, but when it comes to bulleted lists and other "must read" text, do your audience a favor. Make the text considerably bigger than the minimum size. If you find yourself needing to use the
minimum size most of the time for most of your text, you're probably trying to cram too much information onto each slide.

The 8H Rule also assumes that your audience's vision is normal or nearly so. If you're speaking to an older group, use larger text, or invent the [Insert Your Name Here] 7H Rule of Text Legibility.

Matters of style

In the presentation business, it's what you say AND how you say it that counts. The text style you choose can have a big effect on legibility.

Should you use serif or sans-serif text? Whether one or the other is more legible is still a matter of heated debate. Many feel that a serif typestyle like Times-Roman makes it easier for the eye to distinguish the various letterforms quickly, leading to faster, easier comprehension. Others argue that sans-serif faces like Helvetica are simpler, hence more legible.

Another school of thought holds that the typestyle we see most often is the one we read most easily. Serif text is used more often than sans-serif in newspapers, magazines and advertisements in the U.S. so serif text might be the best choice. In Europe, the situation is probably reversed.

If you're presenting to audiences that wear eyeglasses, I can tell you from personal experience that those of us with astigmatism find serif text much easier on the eyes.

Whichever typeface you choose, avoid the so-called "decorative" faces ... unusual fonts or styles that look like anything from handwriting to the Gutenberg Bible. They're fun and can be useful for emphasis if used sparingly, but they're very hard to read in bouts of more than one or two words at a time. If you can't imagine reading a whole magazine article in a particular face, don't use it in your presentation.

Even if you've settled on several "standard" faces, it's best to limit yourself to one or at most two distinct faces in any single presentation. If you need to emphasize certain words or areas of text, you can always use italic or boldface, or set the text off in a different color, but using too many different faces clutters up your visuals.

No matter what you've heard or seen, setting your text all in capital letters is a bad idea. It looks as though you're SHOUTING.

Besides looking loud, all-caps text is less legible than text in caps and lowercase. We tend to scan whole lines of text at a time when we read, and we recognize common words as much by their overall shapes as by reading the individual letters. Lowercase letters have much more variety of size and form than capitals, and make word shapes more visually distinctive. A line of text in capitals has relatively little variation in the shapes of the words, so we have to read the individual letters. That slows us down and makes harder work of reading.

By the way, if you grew up using a typewriter, remember where the letters are on the keyboard but forget everything else you know about it. When you use use capitalization, underlining and other such typewriterisms for emphasis, it's a real legibility-killer. And it makes your presentation look like something from the beginning of the last century. Larger text sizes, boldfacing or color are far more effective ways of emphasizing particularly important points.

Be a good host

Think of yourself as a host, and your audience as your guests. Go out of your way to make them comfortable and your presentation will be a success. Anything that gets in the way of their comfort needs to be fixed or eliminated.

You wouldn't think of deliberately mumbling your way through a presentation, right? Of course not! It would be ineffectual and downright rude to your audience.

Using hard-to-read slides is the visual equivalent of mumbling. What your audience can't read, they won't read. What they can't see, they won't be as likely to remember. They will remember you, though ... as the one that made that hour or two in the dark such a frustrating and unrewarding experience.

Both you and your audience will benefit when you follow these simple guidelines. You can be that much more certain that your visuals will be clear and concise, understood and remembered.

And now, as promised, the details

I mentioned some general rules of thumb for establishing minimum legible text heights for "average" situations. What does "average" mean, though? And what if you know you'll be making a presentation under sub-average conditions? How can you guarantee that your audience will be able to read your visuals?

The ideal situation is summed up by the 8H Rule: The distance from the screen to the last row of seats should be no more than 8 times the height of the screen. The smallest text should be at least 1/50 the height of the screen. If you meet these two conditions, your audience should be able to read you loud and clear.

The 8H Rule is fine as far as it goes, but it assumes that we have more control over all the variables than is usually the case. What if the room is bigger than we expected? What if the only screen available is dinky? Since we generally don't know all the details in advance, what can we do to give ourselves a little margin of safety?

Some tricks of the trade

First, the variables we have to work with:

Distance to Back Row, or DBR
How far is it from the screen to the last row of seating?

Effective Screen Height, or SH
How tall is the screen? Keep in mind that this might not be the same as the actual screen height. If you're projecting 16x9 slides on a 48" square screen, the full 48" vertical screen height won't be used. Instead, it'll only be 27".

We'll start by reducing the assumptions made by the 8H Rule to an absolute minimum text height for your particular presentation room.

Working from the 8H Rule and dredging up our high school ratio math, end up with DBR/400 as the minimum text height on screen. Find the distance to the back row (in inches) and divide by 400. For example, if you have a 32 foot (or 384 inch) long room, 384/400 gives a minimum text size on screen of about 1 inch. Don't make your text any smaller than that and everybody should be able to read it.

That's all well and good, but when you're creating your slides on the computer, how can you predict how big the text will be on the silver screen? That depends on the screen height, and the text size you choose. You'll need to know the screen height for the next round of calculations.

Since the relationship between the projected text height (PTH) and screen height (SH) is the same as the relationship between your program's text size (TS) and the drawing page height (DPH), we can use a simple ratio to come up with our answer.

TS is to DPH as PTH is to SH, or (TS * SH) / DPH = PTH

Let's say we have a standard 48" x 48" screen in the same 32 foot room. We already know we need the text to be 1" high (PTH=1) and since we're using 16x9 slides, we can project a 27" hight image so SH=27.

PowerPoint's standard 16x9 page height is 7.5", so that's the DPH value.

(1" TS * 27") / 7.5" = 3.6" PTH

So for that very small screen, to get a projected text size of 1" (so that the folks in the very back row can read it easily) you need to set your text to 3.6" or almost 260 point in PowerPoint. That's crazy big. Clearly, you need to find a taller screen or hand out telescopes!

You can use a similar ratio to work out how far you should stand from your computer monitor to judge what the projected image will look like to your audience.

Measure the height (in inches) of your PowerPoint slide as it's displayed on your monitor ... let's call it MH for Monitor Height. We want to solve for X, where X is how far away you need to be from your monitor.

(DBR * MH) / SH = X

If we stick with the same 32 foot (or 384") room, same 27" screen height and assume that the height of the slide on your monitor is 10":

(384 * 10) / 27 = X

From this, it appears that if you stand 142" or between 11 and 12 feet away from your monitor to judge your text size, you'll have a good idea what your slides will look like to the people in the back row.

Take it to the max, not the min

Remember that all these calculations represent the absolute minimum text sizes needed for legibility, not for guaranteed easy reading. Depending on room conditions and the age of your audience, you could be cutting it a bit thin if you rely strictly on the sizes these formulas suggest. Your audience will have an easier time of it (and love you the better for it) if you use larger text sizes whenever possible.

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What if you gave a presentation but nobody watched?
Last update 09 April, 2018
Created: 09 April, 2018