Between the Fenix 8 (47mm) and OnePlus Watch 3, the Fenix 8 (47mm) comes out ahead in battery life and weight, while the OnePlus Watch 3 wins on peak brightness and display size. Overall, the Fenix 8 (47mm) scores 64.3 and the OnePlus Watch 3 scores 53.9 on our Mars Score.
Which should you buy?
The Fenix 8 (47mm) is the clear pick on raw spec strength, leading by 10.4 points on the Mars Score. The margin is wide enough that the underdog only makes sense if its individual strengths line up with what you specifically need.
Pick the Fenix 8 (47mm) if your top frustration with your current device is running out of charge before the day ends — endurance is the lead spec here. The biggest gaps in its favor are battery life, weight, water resistance.
Pick the OnePlus Watch 3 if the display is what you stare at all day — refresh rate, brightness, or sharpness is where the difference will be most visible. Its strongest claims are peak brightness, display size.
Both ship with comparable ecg, cellular, spo2, so those specs don't separate the two — focus on the differences below.
Bottom line: the Fenix 8 (47mm) is the safer default. The other model is the right choice only when its specific advantages line up with your priorities.
Why Garmin - Fenix 8 (47mm) wins
- ▲Battery life — 220.00% more. 384 h vs 120 h.
- ▲Weight — 8.00 g less. 73 vs 81.
- ▲Water resistance — 5.00 ATM more. 10 vs 5.
Why OnePlus Watch 3 wins
- ▲Peak brightness — 120.00% more. 2200 nits vs 1000 nits.
- ▲Display size — 7.14% more. 1.5 " vs 1.4 ".
Spec comparison
Design
| Spec | Garmin - Fenix 8 (47mm) | OnePlus Watch 3 |
|---|---|---|
| Case size | 47 mmlead | 46.5 mm |
| Weight | 73 glead | 81 g |
| Case material | fiber-reinforced polymer | stainless steel |
| Water resistanceⓘ | 10 ATMlead | 5 ATM |
Display
| Spec | Garmin - Fenix 8 (47mm) | OnePlus Watch 3 |
|---|---|---|
| Display size | 1.4 " | 1.5 "lead |
| Always-on display | true | true |
| Peak brightnessⓘ | 1000 nits | 2200 nitslead |
Health & Fitness
| Spec | Garmin - Fenix 8 (47mm) | OnePlus Watch 3 |
|---|---|---|
| ECG | true | true |
| SpO2 | true | true |
| Temperature sensor | true | true |
| Sleep tracking | true | true |
| Blood pressure | false | false |
Battery & Connectivity
| Spec | Garmin - Fenix 8 (47mm) | OnePlus Watch 3 |
|---|---|---|
| Battery life | 384 hlead | 120 h |
| GPS | true | true |
| Cellular | false | false |
| NFC | true | true |
| OS | Garmin OSlead | WearOS |
Frequently asked
Which has longer battery life, Fenix 8 (47mm) or OnePlus Watch 3?+
Fenix 8 (47mm) lasts 384h vs 120h.
Do Fenix 8 (47mm) or OnePlus Watch 3 support ECG?+
Both support ECG.
Which has cellular, Fenix 8 (47mm) or OnePlus Watch 3?+
Neither offers cellular.
Spec-level deep dives
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