Garmin Forerunner 255

Works with: iPhone and Android
Display: MIP, 1.3 in
Case sizes: 45.6 mm
Battery: 14 days
GPS battery: 30 hours
Water resistance: 5 ATM
Weight: 49 g

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Garmin Forerunner 255 at a glance

Battery

Around two weeks

Up to 14 days in smartwatch mode. 30 hours with GPS.
GPS

Multi-band GPS

No maps. Runs and rides without your phone.
Display

MIP, 1.3 in

1.3 in.
Health

Heart, sleep and more

Measures blood oxygen and HRV.
Phone & smart

iPhone and Android

Payments.
Build

5 ATM water rating

49 g.

Garmin Forerunner 255 full specifications

Overview

Brand	Garmin
Model	Forerunner 255
Series	Forerunner

Platform & apps

Works with iPhone and Android phones, running Garmin.

It has an app store for extra apps and watch faces.

Operating system	Garmin
Works with	iPhone and Android
Storage	4 GB
App store	Yes

Display

A memory-in-pixel screen: always on, easy to read in sunlight and very light on the battery.

1.3 in.

Display type	MIP
Screen size	1.3 in
Resolution	260 x 260
Colour display	Yes

Design & durability

A 45.6 mm case weighing 49 g.

Rated 5 ATM: fine for swimming laps and showers.

Case sizes	45.6 mm
Case shape	Round
Dimensions	45.6 x 45.6 x 12.9 mm
Thickness	12.9 mm
Weight (case)	49 g
Bezel material	fiber-reinforced polymer
Lens	Corning Gorilla Glass 3
Band material	silicone
Band width	22 mm
Band fitting	22 mm quick release
Fits wrists	130-205 mm
Water resistance	5 ATM

Battery

Around two weeks: up to 14 days in smartwatch mode.

With GPS on, up to 30 hours, or 16 hours in multi-band mode. Makers test with their own settings, so treat these as best-case figures.

Battery (smartwatch mode)	14 days
Battery (GPS)	30 hours
Battery (multi-band GPS)	16 hours
All battery modes	Smartwatch: 14 days; GPS: 30 hours; All satellite systems: 25 hours; Multi-band GPS: 16 hours
Battery type	Lithium ion
Charging	proprietary-plug

GPS & navigation

Built-in multi-band GPS for accurate tracks, even near tall buildings and trees.

Navigation shows a breadcrumb trail, not a full map.

GPS	Built-in
Multi-band GPS	Yes
Satellite systems	GPS, GLONASS, Galileo, QZSS, BeiDou
Automatic GNSS mode	Yes
Maps	Breadcrumb trail
Navigation features	point-to-point navigation, back-to-start, TracBack, Up Ahead, course guidance, projected waypoint

Health & sensors

Tracks heart rate around the clock, plus blood oxygen and HRV.

For sleep, it offers sleep coaching.

Sensors	optical HR, SpO2, barometer, compass, gyroscope, accelerometer, thermometer
Heart-rate sensor	Garmin Elevate
Heart-rate tracking	24/7
High/low heart-rate alerts	Yes
Heart-rate variability	Yes
Blood oxygen (SpO2)	Yes
Respiration rate	Yes
Sleep tracking	Sleep coaching
Stress tracking	Yes
Energy score	Body Battery
Cycle tracking	Yes

Safety

Has an emergency SOS feature.

SOS works through your paired phone. Live tracking lets friends follow your workouts.

Emergency SOS	Via phone
Incident detection	Yes
Live tracking	Yes

Training

Built for training, with the metrics serious athletes use.

It adds a triathlon mode, running power and daily suggested workouts.

Auto activity detection	Yes
Triathlon / multisport	Yes
Swim tracking	Pool and open water
Underwater heart rate	Yes
Training metrics	VO2 max, training load, training effect, recovery time, race predictor, lactate threshold, HRV status, training status
Adaptive coaching	Yes
Running dynamics	Yes
Wrist running power	Yes
Strength rep counting	Yes
Heart-rate broadcast	Yes
External sensors	ANT+, Bluetooth HR strap, power meter, foot pod, speed/cadence, bike radar/lights
Smart trainer control	Yes

Smart features

Smart extras include contactless payments.

Notifications	Yes
Message replies	Android
Contactless payments	Yes
Payment service	Garmin Pay
Find my phone	Yes

Specs compiled from Garmin's product pages and datasheets. Manufacturers revise hardware between versions, so check the version on the box. Spotted an error? Tell us.