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Head to head

Garmin Garmin fēnix 9 43mmvsGarmin Garmin fēnix 9 51mm

Released
2026-08-25Garmin newsroom — fēnix 9 and fēnix 9 Pro, retrieved 2026-09-13
Price
£859.99Garmin UK store — fēnix 9 43 mm, retrieved 2026-09-22
Security updates until
2028-08-25Garmin UK — fēnix 9 (Security Information), retrieved 2026-09-22
Released
2026-08-25Garmin newsroom — fēnix 9 and fēnix 9 Pro, retrieved 2026-09-13
Price
£949.99Garmin UK store — fēnix 9 51 mm, retrieved 2026-09-22
Security updates until
2028-08-25Garmin UK — fēnix 9 (Security Information), retrieved 2026-09-22

1 win for Garmin fēnix 9 43mm1 win for Garmin fēnix 9 51mm0 differences you won’t notice£90 apart at RRP

Verdict: Garmin fēnix 9 43mm ahead on 1 row, Garmin fēnix 9 51mm on 1 row

On the makers’ published figures, the Garmin fēnix 9 43mm wins on weight (case only) (44 g against 65 g); the Garmin fēnix 9 51mm wins on battery life (maker's claim) (696 h against 240 h). The other 10 rows have no threshold or no direction to judge by, so nobody wins them.

Specifications

A win is marked only where the figures can be ranked and the gap is one you could notice on the wrist. A row the site has no threshold for says whether the two differ, and that it is not ranking them. = marks the same figure on both, ≠ not ranked a difference with no ranking. Every figure carries its source.

Body

SpecificationGarmin fēnix 9 43mmGarmin fēnix 9 51mm
Case size
43mmOfficial
51mmOfficial
Case shapeSame.
roundOfficial
roundOfficial
Weight (case only)
44gOfficialwins this row
65gOfficial

Garmin fēnix 9 43mm is ahead here, by a gap you’d notice.

Water ratingSame.
10 ATM; 4 ATM Dive (EN 13319)Official
10 ATM; 4 ATM Dive (EN 13319)Official

Display

SpecificationGarmin fēnix 9 43mmGarmin fēnix 9 51mm
Display typeSame.
AMOLEDOfficial
AMOLEDOfficial
Display sizeDiffers, but not ranked.
1.3inOfficial
1.4inOfficial

Battery

SpecificationGarmin fēnix 9 43mmGarmin fēnix 9 51mm
Battery life (maker's claim)
10 days (240 h)hOfficial
29 days (696 h)hOfficialwins this row

Garmin fēnix 9 51mm is ahead here, by a gap you’d notice.

Health

SpecificationGarmin fēnix 9 43mmGarmin fēnix 9 51mm
SensorsSame.
Garmin Elevate wrist heart rate monitor, Pulse Ox blood oxygen saturation monitor, barometric altimeter, compass, gyroscope, accelerometer, thermometer, ambient light sensor, depth sensor (to 40 m)Official
Garmin Elevate wrist heart rate monitor, Pulse Ox blood oxygen saturation monitor, barometric altimeter, compass, gyroscope, accelerometer, thermometer, ambient light sensor, depth sensor (to 40 m)Official
GPSSame.
GPSOfficial
GPSOfficial

Connectivity

SpecificationGarmin fēnix 9 43mmGarmin fēnix 9 51mm
Cellular modelSame.
NoOfficial
NoOfficial

Compatibility

SpecificationGarmin fēnix 9 43mmGarmin fēnix 9 51mm
Works withSame.
Compatible with iPhone and AndroidOfficial
Compatible with iPhone and AndroidOfficial
CompatibilitySame.
iPhone and AndroidOfficial
iPhone and AndroidOfficial
23 attributes neither watch has a sourced figure for

Dimensions · Case material · Strap width · Display area · Resolution · Peak brightness · Always-on display · Operating system · Chip · Storage · RAM · Battery capacity · Charge to 80% · Charging · ECG · Blood oxygen · Skin temperature · Blood pressure · Cellular model price · UK networks with eSIM · Wi-Fi · Bluetooth · NFC payments. Rows appear as sources are cited — a gap in our data, not a statement about either watch.

The pairs a buyer of either watch would also weigh. Any two watches in the catalogue can be compared from the chooser.