# How big does the text have to be?

> There is a number for this and you can get it with a tape measure. The sign trade's rule of thumb converted into the one figure you actually type into a slide, plus the checks that decide whether the board reads from the door.

Source: https://channelos.tv/academy/how-big-the-text-has-to-be
Published: 2026-10-29
Track: Make the board worth looking at
Lesson 1 of 4
Plan: Free plan
Author: The ChannelOS team

**Text on a digital sign needs roughly 25mm of capital-letter height for every 3 metres a person stands back. That is a trade rule of thumb, not a standard. On a ChannelOS slide every size is a percentage of the slide's width, so the number to type is about 54 times the distance in metres divided by the screen's diagonal in inches: a 55 inch screen read from 4 metres wants about 4. Use 96 on a portrait board.**

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## The short version, in 5 steps

1. Measure from the screen to the furthest person who has to read the board.
2. Multiply that distance in metres by 54 and divide by the screen's diagonal in inches, using 96 instead of 54 on a portrait board.
3. Set the item name to that size in the editor, rounding up rather than down, and put headings above it.
4. Keep every face at Medium weight or heavier, and reserve capitals for two or three words.
5. Stand where you measured from and read the board out loud, or photograph it from there and look at the photo.

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The board looked right. Then you walked to the door, turned round, and the prices had gone to grey smudges. Nothing had changed on the screen: the board was drawn on a laptop 50 centimetres from your face and it is read from six metres away across a room. Those are two different jobs and only one of them was done.

**The sign trade's rule of thumb is about 25mm of capital-letter height for every 3 metres a person stands back**, which is roughly 8mm per metre. It describes a comfortable glance rather than a standard, so treat it as a floor and round up, never down.

## How do I turn that into the number in the editor?

The rule is in millimetres on glass. What you set is a size on a slide. Three facts convert one into the other, and the whole thing fits in your head.

Every length on a ChannelOS slide is a percentage of the slide's **width**, so a size of 4 means the type is 4% of the board's width whatever the board physically is. Capital height is about 70% of the size you type. And a 16:9 panel is about 22mm wide for every inch of diagonal.

Put those together and one line falls out:

`size = 54 * distance in metres / screen diagonal in inches`

A 55 inch TV read from 4 metres: 54 times 4 is 216, divided by 55 is 3.9, so set the item name to 4.

| Screen | Furthest read | Landscape size | Portrait size |
|---|---|---|---|
| 43 inch | 3 m | 3.8 | 6.7 |
| 55 inch | 4 m | 3.9 | 7.0 |
| 55 inch | 6 m | 5.9 | 10.5 |
| 65 inch | 8 m | 6.6 | 11.8 |

**On a portrait board the constant is 96, not 54.** Same arithmetic, different width: a quarter-turned 55 inch panel is only about 685mm across instead of 1218mm, so the same percentage buys you far less letter. That 1.78 factor is exactly why a portrait board built by copying numbers across from a landscape one reads as timid, which [designing for the column](/academy/build-a-portrait-show) goes into properly.

If you would rather read a figure off a table than multiply anything, the pixel version by screen size and distance is in [digital menu board design](/blog/digital-menu-board-design), along with the contrast floor.

## What size TV do I need for digital signage?

Turn the formula round. An ordinary multi-line board wants an item name somewhere near 4, which gives you about **13 inches of diagonal per metre of viewing distance**. Four metres wants 55 inches. Six metres wants 80.

That is bigger than most people expect, and the honest answer is that you usually do not buy the bigger screen. You cut the board down instead. A 55 inch screen read from 6 metres is a three line board at size 6, not a menu. Both of those are fine boards; only one of them is a decision rather than an accident, and [three slides, not thirty](/academy/three-slides-not-thirty) is the same trade one level up.

## Is 1080p enough for digital signage?

For text at signage distance, almost always, and the arithmetic says so rather than our preference.

A 55 inch 1080p panel is about 1218mm wide, so its pixels sit 0.63mm apart. The eye resolves detail down to roughly one arcminute, which at 3 metres is 0.87mm. The pixel is already finer than the limit. Past about 2.2 metres on that panel, and past about 3 metres even on a 75 inch one, there is no detail you could see that a 4K screen would have drawn differently.

4K earns its place in two spots: a screen read from arm's length, such as a spec board in a showroom, and a fine pitch LED wall. Neither of those is a TV on a wall across a room.

It also does not change the number you set. Because the size is a percentage, one board renders at whatever the panel supplies, so there is no 4K copy of the show to keep in step with the first. The resolution and safe-area half of that is in [the size and resolution guide](/blog/digital-signage-size-guide).

## Why is it still hard to read at the right size?

Because size is only the first of three variables, and the other two are the ones that get skipped.

**Weight.** At six metres you are reading the stroke, not the letter. A Light or Thin face at a given size puts a fraction of the ink on the glass that a Medium one does, and glare plus the panel's own backlight eat into a thin stroke first. Medium is the floor. Below it, making the type bigger does not fix the problem.

**Capitals.** The eye recognises a familiar word partly by its outline, the pattern of ascenders and descenders above and below the line. Set a line in capitals and that outline flattens into a rectangle, so it has to be read letter by letter. Two or three words in caps is a heading. A sentence in caps is a puzzle.

**Contrast.** The 4.5:1 figure everyone quotes comes from web guidance written for a screen an arm's length from your face. A TV on a wall with daylight on it, read off-axis, wants at least 7:1 on an item name and 10:1 on a price.

## How do I check it without walking back and forth?

Stand where the furthest person stands and read the board out loud. If you hesitate on a word, it is too small. That is the whole test and it costs thirty seconds.

![A ChannelOS digital menu board](/shots/digital-menu-board-template.webp)

Then the cheap version for when you cannot get back there: **photograph the screen from that spot on your phone and look at the photo.** It works for two reasons that have nothing to do with the camera. A phone photo shrinks the board to a thumbnail, which is a decent stand-in for reading it from further away. And it takes you out of the room, so you judge the letters instead of remembering what they say, which is the thing you cannot stop doing while standing in front of your own work.

## When the arithmetic is the wrong answer

Three cases where the formula stops being the thing to follow.

**Small print is exempt.** Allergen notices, terms, licence numbers and opening hours are read at the counter from half a metre, not from the queue. Size those off the furthest read and the board shouts, crowding out whatever you are actually selling.

**A board read while moving wants roughly double.** The rule of thumb assumes a standing reader taking a comfortable glance. Somebody walking past a window, or a car in a drive-through lane, gets a fraction of a second and no second look.

**And if the screen is not a 16:9 panel, none of this converts.** Both the 22mm per inch and the 54 come straight out of 16:9 geometry. A shelf-edge strip, a stitched video wall or a bespoke LED array has its own pixel map, ChannelOS does not author in those shapes, and the wall controller's own software is the better tool for them.

## Do the measurement, then set one number

Measure from the screen to the furthest person who has to read it, multiply by 54, divide by the diagonal in inches, and set the item name to that. Then go and stand there.

The screen already in the room is enough to try it on, and the first one is free for ever, banner and all: a free screen carries a ChannelOS banner that opens into a full ChannelOS slide for about 30 seconds every couple of minutes, and any paid plan removes both. If you would rather lay a board out at the real proportions before anything goes near a wall, the [menu board maker](/tools/menu-board-maker) needs no account at all.

## Frequently asked questions

### How big should text be on a digital sign?

Work back from the furthest person who has to read it. The sign trade's rule of thumb is about 25mm of capital-letter height for every 3 metres of viewing distance, roughly 8mm per metre, which is a comfortable glance rather than a standard, so round up. On a ChannelOS slide that converts to a size of about 54 times the distance in metres divided by the screen's diagonal in inches. A 55 inch screen read from 4 metres wants about 4.

### How far away can you read a TV screen?

It depends on how many lines are on it, because distance and item count trade against each other. For a multi-line board with an item name around size 4, a usable rule is about one metre of viewing distance for every 13 inches of diagonal, so a 55 inch screen tops out near 4 metres. Strip the same board back to two or three lines at size 8 and it reads from roughly twice that. Nothing about the screen changed, only what you asked it to carry.

### What size TV do I need for digital signage?

Turn the sizing rule round and you get roughly 13 inches of diagonal per metre of viewing distance for an ordinary multi-line board: about 55 inches at 4 metres, about 80 inches at 6. That is larger than most people expect, and the usual answer is not to buy the bigger panel. Cut the board down to fewer lines at a bigger size instead, which costs nothing and is a decision rather than an accident.

### Is 1080p enough for digital signage?

For text read across a room, almost always. A 55 inch 1080p panel puts its pixels 0.63mm apart, and the eye resolves detail down to about one arcminute, which at 3 metres is 0.87mm. The pixel is already finer than the limit, so past roughly 2.2 metres on that panel there is no detail a 4K screen would have drawn differently. 4K earns its place at arm's length, such as a showroom spec board, and on a fine pitch LED wall.

### Why does my board look fine on my laptop and not on the wall?

Because a laptop is 50cm from your face and the wall is six metres from the customer, so the design was judged at the wrong distance. Three things then fail in order: the type is too small for the furthest read, the face is too light, because at distance you are reading the stroke rather than the letter, and the contrast was set for a screen with no daylight on it. Size is only the first of the three.


## Next lesson

[Three slides, not thirty](https://channelos.tv/academy/three-slides-not-thirty)


## Further reading

- https://channelos.tv/blog/digital-menu-board-design
- https://channelos.tv/blog/digital-signage-size-guide
- https://channelos.tv/tools/menu-board-maker


The whole curriculum: https://channelos.tv/academy and https://channelos.tv/academy.md