Garmin Forerunner 45 vs Garmin Forerunner 645

Every spec side by side, from each maker's published figures.

Only show differences

Better figure, where one is clearly better

Share comparison

Forerunner 45 compared with Forerunner 645

	GarminForerunner 45	GarminForerunner 645
Overview
Released
Released	May 2019	2018
Display
Case sizes
Case sizes	42 mm	42.5 mm
Panel
Panel	Memory-in-pixel	Memory-in-pixel
Always-on display
Always-on display	Yes	Yes
Display detail
Display detail	1.04-inch (26.3 mm) sunlight-readable colour MIP display, 208 x 208 pixels, with button controls.	1.2-inch (30.4 mm) sunlight-readable transflective colour MIP display, 240 x 240 pixels, with five-button control.
Screen protection
Screen protection	Chemically strengthened glass.	Chemically strengthened glass.
Health and fitness
ECG
ECG	No	No
Blood oxygen
Blood oxygen	No	No
Skin temperature
Skin temperature	No	No
Sleep apnoea alerts
Sleep apnoea alerts	No	No
High blood pressure alerts
High blood pressure alerts	No	No
Body composition
Body composition	No	No
Fall detection
Fall detection	No	No
Crash detection
Crash detection	No	No
GPS
GPS	Single-band	Single-band
Water resistance
Water resistance	50 m	50 m
Sensors
Sensors	GPS, GLONASS, Galileo, Garmin Elevate wrist heart rate and accelerometer.	GPS, GLONASS, Garmin Elevate wrist heart rate, barometric altimeter, compass, gyroscope, accelerometer and thermometer.
Health features
Health features	All-day heart rate, stress and sleep tracking, plus Body Battery energy monitoring.	All-day heart rate, steps, sleep and intensity minutes.
Fitness features
Fitness features	Garmin Coach, VO2 max estimate, running and cycling profiles, indoor track, treadmill, elliptical, cardio and yoga activities.	Running, indoor running, cycling, pool swimming, skiing and rowing profiles; training status and load, aerobic and anaerobic training effect, VO2 max, recovery time and breadcrumb course guidance. Detailed running dynamics require an HRM strap or Running Dynamics Pod.
Safety features
Safety features	Incident detection, assistance and LiveTrack require a paired phone.	–
Battery and connections
Battery life (maker's claim)
Battery life (maker's claim)	Up to 7 days	Up to 7 days
Mobile data option
Mobile data option	No	No
Works with
Works with	iPhone and Android	iPhone and Android
Battery life detail
Battery life detail	Up to seven days in smartwatch mode or 13 hours in GPS mode.	Up to seven days in smartwatch mode or 14 hours in GPS mode per the exact model's Garmin specification table. The same page's prose says 12 GPS hours; its table and headline say 14.
Charging
Charging	Rechargeable battery with Garmin charging cable.	Rechargeable battery with Garmin charging cable.
Connectivity
Connectivity	Bluetooth and ANT+; smart notifications, phone music controls and Connect IQ watch faces. No on-watch music storage.	Bluetooth, ANT+ and Wi-Fi; Garmin Pay, smart notifications, Connect IQ, LiveTrack and phone music controls. No on-watch music storage.
Storage
Storage	–	Stores 200 hours of activity history.
Design
Weight (lightest version)
Weight (lightest version)	36 g (better)	42.2 g
Software
Software	Garmin	Garmin
Case materials
Case materials	Silicone band and 5 ATM water rating.	Stainless steel bezel, chemically strengthened glass and silicone band; 5 ATM water rating.
Size
Size	42 x 42 x 11.4 mm; 36 g.	42.5 x 42.5 x 13.5 mm; 42.2 g.
Bands
Bands	Fits wrists 129–197 mm.	Quick-release 20 mm band; fits wrists 127–204 mm.
Colours
Colours	Lava red band with black case.	Black band with silver-toned bezel.