Gear Review: Garmin Forerunner 645 Music

The Garmin Forerunner 645 Music GPS running watch is a powerhouse training device that improves the way you work out.

The Forerunner 645 Music and the slimmed down Garmin Forerunner 35 sit in the sweet spot of the Garmin running watch lineup between the streamlined Garmin vivo series and the souped up Garmin fenix series watches. With GPS tracking, heart rate monitoring and the ability to load up to 500 songs, it will boost your knowledge of how you run so you can fine-tune your training.

Compared with other Garmin running watches, we think the 645 is ideal for any runner looking to boost their fitness.

In this Garmin Forerunner 645 Music review, we’ll give you the low-down on the watch’s hardware, software and what our Fleet Feet testers thought about the device.

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The Garmin forerunner 645 Music with a red band


Garmin designed the Forerunner 645 Music to go with you wherever—or whenever—you run.

The GPS watch has a slim profile, and the 1.2-inch diameter face is large enough to read while on the move without being cumbersome on smaller arms. In dark situations, the watch uses an activity-activated backlight to illuminate the watch face when you tilt your wrist—one Fleet Feet tester loved the touch-free ability to keep track of his time and pace during a nighttime fartlek.

To house the internal hardware, Garmin sourced chemically strengthened glass and rugged stainless steel that give the watch a minimal, modern look, and they made it waterproof so it’s safe to wear while swimming or showering. Designers also fit the timepiece with interchangeable, quick-release Garmin watch bands made of supple and durable silicone. One wearer said the band felt really soft and comfortable against her wrist, and its low profile stayed out of the way.

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Physical specs:

  • Display size diameter: 1.2 inches (30.4mm)
  • Weight: 42.2 g
  • Fits wrist circumferences from 5-8 inches (127mm to 204mm)

Garmin says the battery lasts up to seven days in smartwatch mode and up to five hours in GPS mode with music. One tester found the watch got about four to five days of juice when switching between GPS tracking during multiple three to five mile runs without music and regular smartwatch mode when not exercising.

Battery life will vary widely depending on how a runner uses the watch. Runners who cover more miles, stream music and frequently interact with the interface will drain the battery faster than runners who log shorter activities without music.

A woman sets her Garmin Forerunner 645 Music watch


Developers loaded the Garmin watch with features that will satisfy most runners.

First and foremost, the Forerunner 645 Music is a GPS running watch. Outfitted with GPS and GLONASS connectivity, a Fleet Feet tester found the watch quickly picked up a satellite signal and accurately tracked distance, pace, time and elevation changes on his run runs. The watch was sometimes slower to find a satellite signal around tall buildings or under dense tree coverage, though that’s an inherent limitation with any GPS device.

The data is accessible through the watch’s own interface, or you can sync your watch to Garmin Connect—Garmin’s own online running community—or Strava to view your recent and historical data. One tester used the watch face for a quick overview of his runs while cooling down but tracked larger training trends in the accompanying app.

Garmin also integrated a wrist-based heart rate monitor into the back of the watch to give a real-time look at how hard you’re working.

To get the most accurate heart rate reading, the watch needs to be worn above the wrist bone—not between your wrist bone and hand—with its back flush against your skin. One tester noted inconsistent readings when the watch wasn’t properly positioned, but the readings returned to normal when the watch band was tightened up.

While the Forerunner 645 Music packs plenty of features to use for everyday training and races, athletes with more off-the-grid goals should check out the Garmin fenix series GPS watches, which include additional navigation and weather tracking features.


The Garmin Forerunner 645 Music is a practical and stylish Garmin GPS running watch that delivers a trove of activity data without the need for additional devices. With accurate run tracking, heart rate monitoring and app integration, most runners will find the 645 Music does everything they need to train smarter.

Still not convinced? Don’t sweat it. Fleet Feet's return policy means you can test drive your shoes and gear without risk. If you’re not happy with the way your gear performs, looks or fits, we’ll take it back within 60 days. Plus, you’ll get free return shipping on all orders. That's our Happy Fit Guarantee.

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