Garmin · 2018
Forerunner 645Size, Dimensions & Wrist Fit
The Garmin Forerunner 645 sits best on flat wrist widths of about 45–61mm (≈ 12.0–16.3cm wrist circumference). Adjust the slider below to check your wrist.
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The Forerunner® 645 in short
The figures that decide whether this watch suits you, pulled out of the full specification sheet further down.
- Rated for 14 hours of use per charge.
- 13.5mm thick. Thicker than 68% of 43mm watches — it will sit noticeably high on the wrist.
- 1.2" (30.4 mm) diameter display.
- Corning® Gorilla® Glass 3 case, Corning® Gorilla® Glass 3 glass.
Does the Forerunner 645 fit your wrist?
Drag the slider to your wrist width and see the Forerunner 645 overlaid at true scale. Lug-to-lug — not case diameter — decides whether a watch overhangs your wrist.
Watch Fit Tool
For sports watches, lug-to-lug (L2L) is what matters most — it decides whether a watch overhangs your wrist. Bulky is fine; overhang is not.
Measure at the point where you wear your watch — typically just below the wrist bone.
Flat width — lay your arm on a table, palm facing up, and measure straight across the top of your wrist with a ruler. Bone to bone; do not follow the curve down the sides.
Around — wrap a tape measure snugly round the wrist. No tape? Wrap a strip of paper, mark the overlap and hold the strip against a ruler.
Width ≠ circumference. They are different numbers — around 170mm is about 64mm across — so set the toggle to whichever one you actually measured before you type it in.
Garmin Forerunner® 645
Case 42.5mm · Lug-to-lug 42.5mm · Thickness 13.5mm · 42g
Balanced Fit
42.5mm on a 55mm wrist
Across the wrist it works — 6.3mm spare each side — but a tall watch on this wrist. Fine over a sleeve, awkward under one.
On a 55mm wrist the sweet spot is 47–53mm lug to lug. This one is 42.5mm, so you could go bigger.
Measure where you wear it, just below the wrist bone. Either of these works — the tool converts between them.
- 1. Flat width — arm flat on a table, palm up. Measure straight across the top of the wrist, bone to bone, ignoring the curve down the sides.
- 2. Around — a tape, or a strip of paper marked and held against a ruler, snug the whole way round.
Leather: Attaches at the lugs, so the case back rests on your skin. Thins and softens with wear. Typical figures, not this model’s own.
Show the measurementsHide the measurements
- Across the wrist6.3mm spare each side
Comfortable, with visible skin either side.
- Off the wrist13.5mm off the skin
A tall watch on this wrist. Fine over a sleeve, awkward under one. (13.5mm case, back against the skin)
- How it seats~4.2mm under the rim
Seats well, with the case back following most of the wrist.
- Weight on the wrist42g
Light enough to forget you have it on. (0.8g per mm of wrist)
Happy with the fit? Check current availability for the Forerunner 645.
Check offer2D Dimension Schematics
The Forerunner® 645 drawn to scale — from above, and in profile against the wrist.
- Garmin Forerunner® 64542.5mm · 13.5mm thick
3D preview
Garmin Forerunner® 645 on a wrist
On an arm sized to your own wrist — the view a product photo never gives you.
Shapes are built from published measurements, not manufacturer 3D models — accurate proportions, generic dial.
Forerunner® 645 battery life
The runtime the manufacturer publishes for everyday use.
- Smartwatch14 hours
How the Forerunner® 645 ranks on battery
Against the 296 Garmin watches in our database, ranked on each figure Garmin publishes.
- Everyday use7 days#241 of 285
- GPS tracking14 hours#223 of 267
Forerunner® 645 specifications
The figures that decide a purchase, followed by every line Garmin publishes.
- Battery life
- Smartwatch Mode: Up to 7 daysGPS mode: Up to 14 hours
- Display
- 1.2" (30.4 mm) diameter
- Resolution
- 240 x 240 pixels
- Bezel
- stainless steel
- Glass
- Corning® Gorilla® Glass 3
- Strap
- silicone
- Storage
- 200 hours of activity data
Full specification sheet
136 published lines across 17 groups, unedited
Overview
- Family
- Garmin
General
- Battery life
- Smartwatch Mode: Up to 7 daysGPS mode: Up to 14 hours
- Display Size
- 1.2" (30.4 mm) diameter
- Color display
- Lens Material
- Corning® Gorilla® Glass 3
- Bezel Material
- stainless steel
- Memory/History
- 200 hours of activity data
- Strap material
- silicone
- Display resolution
- 240 x 240 pixels
- Quick Release bands
- yes (20 mm, Industry standard)
Sensors
- GPS
- Compass
- GLONASS
- Galileo
- Gyroscope
- Thermometer
- Accelerometer
- Barometric altimeter
- Garmin Elevate™ wrist heart rate monitor
Product Info
- Main SKU
- 010-01863-00
- Product ID
- 591311
- Product Name
- Forerunner® 645
- Release Date
- 1/9/2018
- Product Variation
- Black with Stainless Hardware
Clock Features
- Timer
- Stopwatch
- Time/date
- Alarm clock
- GPS Time Sync
- Sunrise/sunset times
- Automatic daylight saving time
Cycling Features
- Courses
- Race an activity
- Compatible with Varia™ lights
- Speed and cadence sensor support (w/sensor)
- Compatible with Varia™ radar (rear-facing radar)
- Compatible with Varia Vision™ (head-mounted display)
- Alerts (triggers alarm when you reach goals including time, distance, heart rate or calories)
Running Features
- Run workouts
- Race predictor
- Foot pod capable
- Running dynamics
- Performance condition
- GPS-based distance, time and pace
- Cadence (provides real-time number of steps per minute)
What You'll Love
- Garmin Pay™
- Training status
Activity Profiles
- Gym
- Strength, Cardio and Elliptical Training, Stair Stepping, Floor Climbing, Indoor Rowing and Yoga
- Swim
- Pool Swimming
- Cycling
- Biking, Indoor Biking
- Outdoor recreation
- Skiing, Snowboarding, XC Skiing, Stand up Paddleboarding, Rowing
Swimming Features
- Pool swim workouts
- Drill logging (pool swim only)
- Countdown start (pool swim only)
- "Repeat on" rest timer (pool swim only)
- Basic rest timer (up from 0) (pool swim only)
- Stroke type detection (freestyle, backstroke, breaststroke, butterfly) (pool swim only)
- Pool swim metrics (lengths, distance, pace, stroke count, swim efficiency (SWOLF), calories)
Outdoor Recreation
- TracBack®
- Back to start
- UltraTrac mode
- Vertical speed
- GPS coordinates
- Elevation profile
- Total ascent/descent
- Distance to destination
- Point-to-point navigation
- Bread crumb trail in real time
Daily Smart Features
- Calendar
- Connectivity
- Bluetooth®, ANT+®, Wi-Fi®
- Find My Phone
- Find My Watch
- VIRB® Remote
- Weather forecasts
- Smart Notifications
- Smartphone compatibility
- iPhone® and Android™
- Controls smartphone music
- Pairs with Garmin Connect™ Mobile
- Text response/reject phone call with text (Android™ only)
- Connect IQ™ (downloadable watch faces, data fields and apps)
Activity Tracking Features
- TrueUp™
- Move IQ™
- Step counter
- Floors climbed
- Calories burned
- Distance traveled
- Intensity minutes
- Automatic rep counting
- Garmin Connect™ Challenges app
- yes (optional Connect IQ app)
- Move alerts (displays on device after a period of inactivity)
- Auto goal (learns your activity level and assigns a daily step goal)
Workout and Training Plans
- Cardio workouts
- Strength workouts
Health & Wellness Monitoring
- Sleep
- yes (advanced)
- Hydration
- yes (in Garmin Connect™ and optional Connect IQ™ widget)
- Fitness age
- yes (in app)
- All-day stress
- Women's health
- yes (in Garmin Connect™ and optional Connect IQ™ widget)
- Resting heart rate
- Relaxation breathing timer
- Wrist-based heart rate (constant, every second)
Kid Activity Tracking Features
- Toe-to-Toe™ Challenges app
- yes (optional Connect IQ Toe-to-Toe™ Challenges app)
Training, Planning and Analysis Features
- % HRR
- % HR max
- HR zones
- HR alerts
- Manual lap
- Auto max HR
- Auto scroll
- Finish time
- HR calories
- Voice alerts
- Custom alerts
- Physio TrueUp
- Recovery time
- Training load
- VO2 Max (Run)
- Course guidance
- Training effect
- Virtual Partner
- Race an Activity
- Advanced workouts
- Interval training
- Garmin Live Segments
- Strava Live Segments
- GPS speed and distance
- Configurable lap alerts
- Customizable data pages
- Touch and/or button lock
- Activity history on watch
- Downloadable training plans
- Training effect (anaerobic)
- Customizable activity profiles
- Auto Pause® automatic timer halt
- Auto Lap® interval tracking feature
- HR broadcast (broadcasts HR data over ANT+® to paired devices)
Alternatives to the Forerunner® 645
Watches that cover a similar amount of wrist, with the measurements that separate them.
Garmin
Forerunner® 645 Music
- Width
- 42.5mm
- Thick
- 13.5mm
- Weight
- 42.2g
Garmin
Forerunner 70
- Width
- 42.6mm
- Thick
- 11.9mm
- Weight
- 40g
Garmin
Forerunner 170
- Width
- 42.6mm
- Thick
- 11.9mm
- Weight
- 41g
Garmin
Forerunner 170 Music
- Width
- 42.6mm
- Thick
- 11.9mm
- Weight
- 41g
Garmin
Forerunner® 570 - 42mm
- Width
- 42.4mm
- Thick
- 12.9mm
- Weight
- 42g
Garmin
Forerunner® 245
- Width
- 42.3mm
- Thick
- 12.2mm
- Weight
- 38.5g
Forerunner® 645 — Frequently Asked Questions
Will the Garmin Forerunner 645 fit my wrist?
The Garmin Forerunner 645 looks balanced on flat wrist widths of roughly 45–61mm (about 12.0–16.3cm circumference). Drag the slider above to check it against your own measurement.
How long does the Garmin Forerunner 645 battery last?
Garmin rates it at 14 hours per charge in everyday use.
How does the Garmin Forerunner 645 battery compare with other Garmin watches?
At 7 days in everyday use it ranks #241 of the 285 Garmin watches in our database — below the middle of the range. The full ranking, including GPS and power-saving figures, is on our Garmin battery life comparison.
Is the Garmin Forerunner 645 thick for a 43mm watch?
At 13.5mm, thicker than 68% of 43mm watches — it will sit noticeably high on the wrist. Thickness, not case width, is what decides whether a watch catches on a shirt cuff.
What other watches are the same size as the Garmin Forerunner 645?
OnePlus Watch 3 43mm, Oppo Watch X2 Mini, Omega Speedmaster Moonphase Stainless Steel / Black Meteorite / Bracelet, Zenith Defy Extreme Diver Shadow / Bracelet all sit within half a millimetre of the Garmin Forerunner 645's 42.5mm case, so they cover the same amount of wrist.
