QR Code Not Scanning? How to Find the Cause Step by Step

The cause is in one of three places

When a QR code won't scan, remaking it straight away is the long way round. A QR code goes through three stages: turning data into a picture, putting that picture on paper or a screen, and reading it with a camera. Find which stage is broken first, and you have just one thing to fix.

The quickest test is to show the QR code large on a computer screen and scan it with your phone. If it scans there, the data itself is fine and the problem lies in printing, size or the reading conditions. If it won't scan even on screen, go back and review the settings you used to make it.

Four settings that often go wrong when making the code

At the making stage, these four things usually cause the trouble. The first, the amount of data, is easy to miss by eye but has a big effect.

1. 1

   1. Put in fewer characters

   The more data a QR code holds, the finer its grid of squares (modules) becomes, and the harder it is to read at the same printed size. Trimming parameters off long URLs or using a short sharing URL is the most effective fix.

2. 2

   2. Export it at the size you need

   The QR Code Generator lets you set a size from 128 to 1024px. For print, export it large (512px or more). You can always shrink an image later, but you can't enlarge it without losing quality.

3. 3

   3. Keep a dark foreground on a light background

   You can change the foreground and background colours, but if the contrast is low it won't scan. Black on white is the most reliable. If you add colour, make the foreground dark enough.

4. 4

   4. Don't invert light and dark

   Some devices can't read an inverted design with a black background and a white code. It may look stylish, but it is best avoided on anything you hand out.

Size guide for printing and posting

The most common reason a printed QR code won't scan is simply that it is too small. As a rule of thumb, make each side about one tenth of the distance it will be scanned from, and it will read comfortably.

These are minimums. The more characters you put in, the finer the grid gets, so you need to print larger for the same distance. If in doubt, do a test print at full size on the actual paper and check it scans on your phone.

• Glossy paper and lamination can reflect lights and become unreadable. Choose matte paper for posters
• On folded flyers, make sure no fold or crease runs across the code
• On paper where ink bleeds, make the code larger so the squares are bigger
• On curved surfaces such as bottles or pillars, make it about 20% larger than on a flat surface

Problems on the reading side

If the code itself is fine but still won't scan, the cause is the reading conditions. This is easy to miss if you only test on your own device.

How to remake a QR code that scans

1. 1

   1. Make the content as short as possible

   For a URL, drop tracking parameters and unnecessary path levels. For text, keep it to the minimum wording you need.

2. 2

   2. Paste it into the QR Code Generator

   Enter a URL or text and the code is generated on the spot. What you enter is processed in your browser.

3. 3

   3. Set the size for how it will be used

   Aim for 256–512px for screens and 512–1024px for print. Making it large and shrinking it later causes no loss of quality.

4. 4

   4. Try black on white first

   Even if you need to change colours for the design, check that the standard colours scan first, then change them and scan again afterwards.

5. 5

   5. Save as PNG and convert if needed

   PNG suits sharp-edged graphics like QR codes. If the print shop asks for JPEG, convert it with the Image Format Converter and run another scan test on the converted image.

JPEG tends to produce block noise and blurs the edges of fine squares. If you must use JPEG, set a high quality (90% or more) and always scan the converted image to check. The steps for making a code are covered in how to make a QR code, and the problem of codes using short URLs that stop working later is covered in do QR codes expire.

FAQ

Is there a character limit for QR codes?

The standard allows quite a lot of characters, but the more you add, the finer the grid and the harder it is to read. In practice, keeping URLs under 100 characters and text to around 300 gives stable results even in print. If the data is very long, the tool may also fail to generate a code.

Will a QR code still scan if I change its colours?

Yes, as long as the foreground is dark enough and the background light. A good test is that it still separates clearly into dark and light when converted to black and white. Avoid pale-on-pale combinations and inverted designs with a dark background.

It stopped scanning once printed. What should I check?

Size first: make each side at least one tenth of the scanning distance, larger if needed. Next the margin: make sure trimming hasn't removed the white band. If it still won't scan, suspect glare from glossy paper or ink bleed, and do a test print on different paper.

Can I use a QR code I made as many times as I like?

A QR code is just your input turned into a picture, so there is no expiry date or scan limit. But if the URL it links to changes, printed codes will still point to the old URL. If you might need to change the destination, put in a URL you can redirect.