Garmin Forerunner 645 vs Garmin Vivoactive 4 – Comparison

Garmin Forerunner 645 vs Garmin Vivoactive 4 – Comparison

The Forerunner 645 is one of Garmin’s best running watches. The Vivoactive 4 is arguably the best activity that Garmin has ever released. But which one is better to suited to your needs?

Because these watches share a bunch of different features (like running, cycling, swimming and other sports modes), it can be a bit difficult to make the right call. Fortunately, this post will help explain all the key differences and all the the key similarities, with a few recommendations at the end.

Let’s get started.

What are the main differences between the Forerunner 645 and the Vivoactive 4?

  1. Touchscreen  (Vivoactive 4)– The Vivoactive 4 has a touchscreen, whereas the Forerunner 645 relies exclusively on buttons to work the watch. Some runners prefer a ‘button only’ setup. 
  2. Advanced Running Dynamics (FR645) – Only the Forerunner 645 supports advanced running dynamics. This means real time access to cadence, stride length and other valuable running specific metrics.
  3. Garmin Running Power (FR645) – The FR645 supports Garmin running power, the Vivoactive 4 does not. 
  4. Pulse Oximeter (Vivoactive 4) – The Vivoactive 4 is built with Garmin’s latest optical heart rate technology, which includes a pulse oximeter to measure your blood oxygen levels. 
  5. Body Battery Score (Vivoactive 4) – Only the Vivoactive 4 includes support for Garmin’s body batter score. This is basically a wholistic stats which combines your sleep data, training data and heart rate data into one unique metric. 
  6. Golf Mode (Vivoactive 4) – This is a big selling point for people who play golf regularly. The Vivoactive 4 is basically an advanced activity tracker, that doubles up as a dedicated golf watch. 
  7. Guided Workouts (Vivoactive 4) – If you want access to guided workouts at the gym, with visual representations of each exercise on the screen, you will need to invest in the Vivoactive 4.

Forerunner 645 vs Vivoactive 4 - Key Similarities

Forerunner 645

Vivoactive 4



Wrist-based HRM

24/7 Activity Tracking

Sleep Tracking

Stress Tracking

Indoor + Outdoor Running

Indoor + Outdoor Cycling

Indoor + Outdoor Rowing

Pool Swimming

Barometric Altimeter


Garmin Running Coach

Music Storage & Apps

Payments from watch

Bluetooth®, ANT+®, Wi-Fi®

Open Water Swimming

Triathlon Mode

Forerunner 645 vs Vivoactive 4 - Key Differences

Forerunner 645

Vivoactive 4

Screen Size

1.2" (30.4 mm) diameter

1.3" (33.0 mm) diameter

Screen Resolution

240 x 240 pixels

260 x 260 pixels

Physical Size

42.5 x 42.5 x 13.5 mm

45.1 x 45.1 x 12.8 mm


42.2 g

50.5 g

Garmin Running Power

Advanced Running Dynamics


Pulse Oximeter

Body Battery Score

Golf Tracking

Guided On Screen Workouts

Total Sports Modes



Smartwatch Battery

7 Days

8 Days

GPS Battery Life

14 Hours

18 Hours

GPS + Music Battery

5 Hours

6 Hours

Comparison of Sports Modes

Forerunner 645 - Sports Modes Vivoactive 4 - Sports Modes
01) Strength Training 01) Strength Training
02) Cardio Training 02) Cardio Training
03) Elliptical Training 03) Elliptical Training
04) Stair Stepping 04) Stair Stepping
05) Floor Climbing 05) Floor Climbing
06) Indoor Rowing 06) Indoor Rowing
07) Yoga 07) Yoga
08) Running 08) Running
09) Treadmill Running 09) Treadmill Running
10) Indoor Track Running 10) Indoor Track Running
11) Skiing 11) Skiing
12) Snowboarding 12) Snowboarding
13) Cross Country Skiing 13) Cross Country Skiing
14) Stand Up Paddleboarding 14) Stand Up Paddleboarding
15) Rowing 15) Rowing
16) Cycling 16) Cycling
17) Indoor Cycling 17) Indoor Cycling
18) Pool Swimming 18) Pool Swimming
19) Walking Mode 19) Walking Mode
20) Golf Mode

Main Reasons To Choose the Forerunner 645

1. It's much better suited to Running Specialists

On the surface, it might seem like the Forerunner 645 and the Vivoactive 4 have similar running capabilities. However, if you dig a little bit deeper, it should be pretty clear that the FR645 is much better equipped to satisfy the interests of veteran runners. There are 2 big advantages that you gain, if you choose the Forerunner 645. 

Running Benefit A - Advanced Running Dynamics

  • Ground Contact Time – The time your foot spends on the ground with each stride. 
  • Ground Contact Balance – Symmetry between left and right foot when running. 
  • Vertical Oscillation – The amount of ‘bounce’ in your running motion. Reducing the amount of bounce in your stride can improve your running efficiency/economy. 
  • Vertical Ratio – the cost-benefit ratio with stride length. This stat can help you find the ideal stride length for setting new a PB, in any distance. 
  • Cadence – Real time cadence metrics,  displayed on your watch
  • Stride Length – Real time stride length data, displayed on your watch

Running Benefit B - Garmin Running Power

This is another key reason for runners to choose the Forerunner 645. When you invest in one of the accessories that opens up advanced running dynamics (Garmin HRM Run or Garmin HRM Tri or Garmin Advanced Running Pod), you also gain access to Garmin’s running power stats. 

This is definitely a big win for runners, because the accessories needed to access running power with Garmin are significantly cheaper than the 3rd party alternatives (Stryd and Runscribe+ specifically). 

2. You prefer Sports Watches that Don't Have Touchscreens

This a big deal for lots of sports people. While there is nothing wrong with the touchscreen of the Vivoactive 4, it can be easier to operate a button only watch like the Forerunner 645 when you are exercising.

It’s fair to say that interacting with a sports watch when running, cycling, swimming or training at the gym can be a bit easier when you are pressing buttons rather than a screen with sweaty fingers. 


Main Reasons To Choose the Vivoactive 4

1. Guided On Screen Workouts

If you want access to guided workouts at the gym, the Vivoactive 4 will be much better suited to your needs. You literally gain access to a bunch of customized workouts, with a visual demonstration of each exercise in your overall workout.

This is one of the key reasons the Vivoactive 4 can be considered a better ‘Fitness Watch’ than the Forerunner 645. It’s also one of the major improvements between the Vivoactive 3 and the Vivoactive 4. 

2. Pulse Oximeter (Blood Oxygen Measurement Device)

The Vivoactive 4 is built with Garmin’s latest optical heart rate moniter (Elavate V3) which includes pulse oximeter. The point of a pulse ox is to measure your blood oxygen levels. This is then used to help calculate your stress levels, body battery score and altitude acclimation if you exercise above sea level. 

3. Body Battery Score

In Garmin’s own words, the whole point of the Body Battery Score is to “see your body’s energy levels throughout the day so you can find the best times for activity and rest.”

In other words, it’s basically an overarching statistic that combines sleep data, training data and heart rate date into one overarching metric than can help you assess your energy levels. 

Unfortunately the accuracy of this statistic isn’t perfect, but it’s still a pretty cool feature and it can help you identify some lifestyle red flags if you do start pushing yourself a bit too hard, and don’t make time for adequate rest. 

4. Touchscreen

This is a key difference between the Forerunner 645 and the Vivoactive 4. While the touchscreen might not be quite as convenient when running or cycling, it is a lot more convenient during everyday use.

Basically, the Vivoactive 4 feels like more of a Smartwatch, because of the touchscreen. Anyone who operates a mobile phone regularly should be pretty comfortable when interacting with this watch.  

5. Dedicated Golf Mode

Naturally this feature is only relevant to golfers, but if you do play 18 holes regularly, this is a massive drawcard for the Vivoactive 4. 

You basically get an amazing fitness watch, that doubles as a dedicated golf watch. You essentially get, yardage to the front, middle and back of the green, yardage to hazards, automatic shot distance tracking, a digital scorecard, and the option view the shape of the green.

All in all, this could be a compelling reason to choose the Vivoactive 4, if you’re big into golf. 

It's better value for money

Given that the Vivoactive 4 often sells for up to 100 dollars less than the Forerunner 645, it’s pretty easy to suggest that you get much better value for money if you opt for the Vivoactive 4. 

It basically has all the features of the FR645 (except advanced running metrics and Garmin running power), together with a whole lot more. 

In other words, it’s actually a better sports watch, and it costs significantly less (when looking at the standard retail price). This could be the ultimate dealbreaker if you’re still on the fence. 

Final Thoughts

In the end, it comes down to this.

Go for the Forerunner 645 if:

  • You’re big into running
  • You don’t like sports watches with touchscreens

Go for the Vivoactive 4 if:

  • You want the more well rounded sports watch
  • You’re happy using a touchscreen
  • You want better value for money

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