What is the read range of passive UHF RFID tags?

There is no one simple answer to this question.  Handheld RFID readers can read RFID tags somewhere between 1 and 50+ feet.  Fixed readers can read RFID tags up to 100+ feet.  Some very large tags that are designed for items like shipping containers are able to achieve a read range of over 100 feet, however, the size of these are the size of a license plate and not practical in most settings.  Read ranges will vary significantly so we will go into the details of what factors affect the range of RFID tags. 

Primary factors of RFID read ranges are: 
1. Type of reader and the antenna on the reader (could be handheld or fixed readers)
2. Type of asset being tagged 
3. Type and size of the RFID tag being used 
4. The environment of the asset 
5. Placement of the RFID tag on the asset 
6. The orientation of the tag based on the reader’s antenna 

Reader/Antenna type 
Fixed readers have more power and will generally have larger antennas compared to a handheld RFID reader, so the effective read range will be greater.  Range depends on the vendor and model, but fixed readers can often read 2-3 times farther than that of handheld RFID readers. 

The antenna on the reader is another important variable that affects the read range.  There are two common types of antennas: circular and linear.  Linear antennas have a focused wave propagation.  These antennas and antennas on an orientation sensitive tag need to all be in the same orientation to achieve maximum range.  For example, if your orientation sensitive tags are in a horizontal orientation, the reader antenna will also need to be in a horizontal orientation.  If they are not the same orientation, the read range might be a fraction of what it was at the same orientation. 

Circular antennas work best when the orientation varies or cannot be controlled. They can read tags at almost any orientation; however, the read range is less than a linear antenna as the wave propagation is not focused. 

Type of asset being tagged 
The material that the asset is made of can have an impact on the read range of a tag.  Some assets may have metal or liquid components, which can interfere with the read range.  Depending on how close the tag is placed to liquid or metal, you could see significant interference.  For example, a tag that reads in free air at 20 feet could potentially have a 6-inch read range (or less) when it is placed on a laptop.  Laptops have a lot of metal underneath the plastic, which causes interference.  If you have assets with metal or liquid components, you will want to evaluate tags specifically designed for work on these assets. 

Type/Size of RFID tag 
There are hundreds of different types of sizes and options to choose from for passive RFID asset tags.  The larger the tag you choose, the larger the antenna will be, meaning it will have a greater read range than a small tag.  There are some exceptions to this rule, especially for tags designed to mount on metal assets.   These tags can be small and still achieve a large read range because they use metal to improve their performance.  Often customers prefer to find the smallest available tag, with the assumption that all tags have the same read range.  They do not realize that those smaller tags are going to have shorter read ranges compared to the larger options. 

Tag Environment 
There are different regulations and limits on reader power and frequency in different countries, which will affect read range.  In Europe, the operating frequency is lower, and they are limited to using less power than in the U.S., so the range for the same tag and type of reader might be reduced in another country. 

Weather conditions can often be a variable on the read range.  For instance, if your asset is exposed to extremes of hot or cold temperatures, humidity, and rain.  All these unpredictable conditions can cause variations in read range. 

Sometimes existing equipment or machinery used can cause interference with your read range, especially equipment that operates at a similar frequency. 

Tag Placement 
Where you place your tag can affect read range.  Some tags that are made for mounting on metal will perform better if they have free air on certain sides of the tag.  When the tag is placed in the center with not a lot of metal, the range can drop.  On assets like computers, laptops, servers, printers, projectors, etc., it may be difficult to know where the metal is on the asset, as the plastic case is covering up the underlying components.  Test your metal mount tags in different areas of your asset, to identify which spot is best for metal mount tags.  Taking the time to find these “sweet spots” can improve your tag read range significantly.  Remember that the spot on one asset may not be the same spot on that same asset for another type of tag, so thorough testing is important. 

The orientation of tag based on the reader’s antenna 
Your tag may perform better when at a horizontal or vertical orientation, depending on the design of the antenna on the tag, and the type of antenna used on the reader.  There are some tags that are designed to be less sensitive to the orientation and often are symmetrical in size instead of the most common asset tag shape, long and thin. 

When your orientation cannot be controlled, try using a circular polarized antenna (more information in #1) or a tag that is not as sensitive to orientation. 

Posted in Asset Tracking