The invisible bubble of space that constitutes each person territory plays a major role in our social life. In his book “The Hidden Dimension” Edward T. Hall elaborates on the distance factor role in animal social life and humans as well. It appears that people use the same distance rules when interacting with objects as well and QR codes are not an exception.

Many times people mention that they were embarrassed to scan a QR code in certain circumstances, or needed to act strangely in order to scan a code. See http://bit.ly/qePtiX and http://blog.directworks.org/?p=610 for such examples, both by the way are excellent examples on how not to use QR codes.

This is when the hidden distance factor enters into the play, a factor that we must be well aware of it if we want a good response for our QR codes.

## Meaningful distances for humans

Four distances are mentioned in Hall book;

- The intimate distance – effectively zero distance

- The personal distance – this is the distance separating members in a no-contact state. It might be considered as the protecting sphere that individuals maintain between their self and others. The length of the arm plays a major role in defining this distance and it ranges between 1.5-2.5 feet (1/2 to 3/4 meters)

- The social distance – this is the distance that people feel comfortable with, in a social gathering. It allows a normal voice communication and it goes between 4-12 feet (1.25-3.6 meters)

- The public distance – this is the distance considered to be well outside any social involvement. This distance goes between 12 feet and above (more than 3.6 meters)

QR codes are encountered in different circumstances, many of them fits into one of these distances.

QR codes for intimate distance contacts are QR codes on objects that are considered to be yours, or are good candidates to be. Sometimes you are at your own when interacting with them and sometimes not. Few examples

-QR codes inside a magazine or newspaper

-QR codes on envelopes mailed to you

-QR codes on business cards ( you can even interact with them from close distance in public)

-QR codes on the menu in a restaurant

-QR codes on supermarket objects

- QR codes on books/DVD covers

These QR codes are expected to be interacted with from a small distance; it can be as small as the camera focus on your device can go.

QR codes that fit into the personal distance are QR codes that are in your arm distance after extending your arm towards them. Examples-

-QR codes on high shelves objects in supermarkets

-QR codes on electrical products in a shop

-QR codes on bus stations

-QR codes in a zoo or museum

QR codes that are expected to be interacted within a social distance are QR codes positioned in places where many people are gathered. Examples-

-Subway wagons

- Inside buses

- Underground stations

- Inside clubs or pubs

- In halls of movie theaters

The last category is QR codes in the public zone. These QR codes go usually on outdoors big signs, in entrance to malls or street advertisement. The most natural way to contact them is from a distance of 12 feet and above. Examples-

- QR codes on T-shirts

- QR codes on sign posts or buildings

Every distance has an equivalent QR code size. For the intimate distance the rule is easily derived from the camera capabilities on mobile devices today. The rule that holds for almost all current devices is that each module of the QR code must be at least 0.028 inch tall, in print.

That means that a QR code version one (21×21) modules must be at least 0.58 inch tall to be able to be read from a very close distance. Note that a version 2 QR code (25×25) must be at least 0.7 inch tall to reach the same effect.

For all other distances where focus is not an issue – the question is – how tall should the QR code be in print in order to be read from the expected distance?

## Distance and QR code size

Fortunately the question is not hard to solve, elementary school math provides all we need to get the answer.

The view angle of camera devices today is between 45-53 degrees (in a 90 degree for a right angle system). Let’s take the 45 degree example, from the fact that tan(45) = 1 we conclude that the height of what we see on the mobile screen is equal to our distance from the object we are aiming to.

So if we are in distance of 3.2 feet we are going to see on our 320 pixels height mobile screen an area height of 3.2 feet. Assuming that every QR code module of a decodable code must be at least a 2 pixels height (which holds for most readers), we get that a version one QR code (21×21 modules) must be at least 42 pixels tall on the screen. 42 pixels out of 320 pixels are 0.13 of screen height. All screen height is represent a 3.2 feet height in reality (in our example) – hence our QR code must be in reality 0.13*3.2 = 0.42 feet or 5.4 inch (12.8 cm).

So for scanning distance of say – 1.5 feet, we need for a version one QR code 2.4 inch height (6 cm). The following table contains the size of QR code in print for the various distances mentioned above.

Scanning distance |
QR Version1 print size |
QR Version2 print size |
QR Version3 print size |
QR Version4 print size |

Personal – 1.5-2.5 feet (45-75 cm) | 2.4 – 4 “ (6-10 cm) |
2.85-4.75″ (7.15-12 cm) |
3.3 – 5.5″ (8.2 – 14 cm) |
3.7 – 6.3 “ (9.5 – 15.8 cm) |

Social – 4-12 feet (1.2-3.6 meters) | 6.3 – 19″ (16-48 cm) |
7.5 – 22.6″ (19 – 57 cm) |
8.7 – 26.2″ (22 – 66 cm) |
9.9 – 30 “ (25 – 75 cm) |

Public 12-25 feet (3.6-7.6 meters) | 19 – 39 “ (48 – 100 cm) |
22.6 – 46.5″ (57 – 120 cm) |
26.2 – 53.8″ (66 – 166 cm) |
30 – 61.3 “ (75 – 157 cm) |

These sizes are calculated assuming the camera view angle is 45 degrees. In case the view angle is a little bigger add until 15% to these sizes (up to 53 degrees). In general the smaller the view angle the closer the object will appear on the screen. Zoom lens use a very small view angle which takes a small portion of what we see and put it in the entire screen – which causes the zoom effect.

Also note that everything here is linear so if you plan for another distance – use same ratio as in the table to get your QR code size in print.

## The other side of the story

All this can be looked at from a different angle. Assume you already printed a QR code in height of X inches and look at his scanning radius. The smaller the versions of the QR code the greater its scanning radius. The following illustration shows the ratio of the scanning radius for different QR code versions, when the QR code height in print is constant.

Let’s look at the area that the scanning radius provides. If a version one QR code at height X covers a Y area, a version two QR code at same height will cover only 70% of area Y while version 4 will cover only 40% of area Y.

This is why using the smaller QR code version for an outdoor ad is so critical. You are losing 60% of your potential audience if you put a QR code of version 4 instead of a version one QR code, while both take exactly the same printing area.

So use capital letters for URL, URL shorteners, low error correction if you do not intend to decorate your QR code.Minimize the version as you can. Life however is not always in black and white and a high version decorated QR code may attract more clicks than a non decorated lower version one.