The FreeStyle Libre 3 is a continuous glucose monitor (CGM) made by Abbott that measures your blood sugar levels around the clock through a small sensor worn on the back of your upper arm. It’s one of the smallest CGMs available, roughly the size of two stacked pennies, and it sends glucose readings to your smartphone every minute without requiring any finger pricks or manual scans. Each sensor lasts up to 15 days before it needs to be replaced.
How the Sensor Measures Glucose
The Libre 3 sensor has a thin filament, just 5.5 mm long and 0.3 mm wide, that sits just beneath the skin’s surface. Rather than measuring sugar in your blood directly, it reads glucose levels in the fluid between your cells, called interstitial fluid. An enzyme on the sensor reacts with glucose in that fluid and generates a tiny electrical current. The stronger the current, the higher your glucose level. The system converts that signal into a number you can read on your phone.
Unlike the earlier Libre 2, which required you to physically scan the sensor with your phone to see your reading, the Libre 3 streams data continuously over Bluetooth. Your glucose number updates every 60 seconds, so you always have a current reading without needing to hold your phone up to the sensor. The app also sends real-time alerts if your glucose goes too high or too low.
Accuracy
In clinical testing, the Libre 3 had an overall accuracy rating of 7.8% MARD, which is the standard metric for CGM precision (lower numbers mean better accuracy). For adults, accuracy was slightly better at 7.5%, while children ages 6 to 17 came in at 8.6%. Younger children ages 4 and 5 showed 10.0% MARD. For context, anything under 10% is generally considered accurate enough for making insulin dosing decisions, so the Libre 3 performs well across age groups.
How It Compares to the Libre 2
The most noticeable upgrade from the Libre 2 to the Libre 3 is size. The Libre 2 Plus sensor is about the thickness of two stacked quarters, while the Libre 3 Plus is noticeably smaller. Both sensors now read glucose every minute, but the Libre 3 was the first in the lineup to offer continuous streaming without scanning. If you used an older Libre 2 sensor (not the “Plus” version), you had to wave your phone over the sensor each time you wanted a reading. The Libre 3 eliminated that step entirely.
Both sensors last 15 days per wear. The practical difference comes down to convenience: the Libre 3’s smaller footprint makes it less visible under clothing, and the automatic streaming means you never miss data because you forgot to scan.
Insulin Pump Compatibility
The Libre 3 works with several automated insulin delivery systems, which use CGM data to adjust insulin doses automatically. Compatible pumps include the iLet Bionic Pancreas, the twiist system, and the Tandem X2. This integration lets the pump read your Libre 3 glucose data and increase or decrease insulin delivery without you needing to intervene, which is particularly useful overnight or during exercise.
Phone and App Requirements
The Libre 3 does not use a separate reader device. Instead, it pairs with the FreeStyle Libre 3 app on your smartphone. The app works on iPhones running iOS 15.6 or later and Android phones running version 10 or later. Not every phone model is supported even if it runs a compatible operating system, so it’s worth checking Abbott’s compatibility list before purchasing.
Cost
The system requires a prescription. For people with commercial insurance, out-of-pocket costs typically range from $0 to $75 per month. That estimate comes from Abbott’s own data on prescription claims and doesn’t reflect what Medicare, Medicaid, or uninsured patients pay. Since each sensor lasts 15 days, a month’s supply means two sensors. Without insurance, the cost is significantly higher, though Abbott offers savings programs for eligible patients.
What Wearing It Is Like
You apply the sensor yourself using a one-piece applicator that presses the sensor and its adhesive patch onto the back of your upper arm. The filament is so thin that most people feel only a brief pinch during application. Once it’s on, the sensor is water-resistant, so you can shower, swim, and exercise without removing it. It sits flat enough against the skin that it’s easy to forget you’re wearing it, though the adhesive can occasionally irritate sensitive skin over the full 15-day wear period. After 15 days, the sensor automatically shuts off, and you peel it off and replace it with a new one.