How big should a QR code powered by GS1 be?

Typically, the space needed for a QR code powered by GS1 will depend on how much data is encoded within it. The longer the URL plus additional data, the more columns and rows of squares are required. 

The size of any barcode is determined by something called the X-dimension. This is the width of the smallest module in the barcode. In the case of a QR code, it’s the size of one of the little squares.  

GS1 has specified (General Specifications - section 5.12.3.1) a minimum and maximum size of this X-dimension for QR codes scanned at retail point of sale as 0.396mm to 0.990mm. This means that at the smallest X-dimension, if your QR code was 29 modules across and included the 4-module width Quiet Zone (blank space) which is required around the outside of the QR code, the total minimum size would be 14.6mm x 14.6mm.  

The amount of space on the pack, scanning environment, the quality of printing and the resolution of the printing process all factor into the optimal X-dimension for a package.

A symbol that is too small may not be easily read by scanners, or it may be difficult to print at a high quality and sufficient resolution. If the QR code is too large, it may be too difficult to scan up close or to print with high enough quality or resolution.  

How do I calculate the minimum size for a GS1 powered QR code created for a product.

The solution provider you are working with to create the QR code image should be able to advise you. To calculate the size yourself: 

Count the number of modules from left to right, add the space created for the Quiet Zone which is 8 modules and then multiply the number of modules by 0.396.

e.g. (29+8) * 0.396 = 14.652mm

(The minimum size for each module, 0.396 has been sourced from the GS1 General Specification for standards compliance).