Between the Watch Ultra 3 and Fenix 8 (47mm), the Watch Ultra 3 comes out ahead in peak brightness and display size, while the Fenix 8 (47mm) wins on battery life. Overall, the Watch Ultra 3 scores 65.3 and the Fenix 8 (47mm) scores 64.3 on our Mars Score.
Which should you buy?
These two are nearly even on the Mars Score (65.3 vs 64.3). The decision isn't about overall quality — both clear the bar — it's about which specific trade-offs fit your use.
Pick the Watch Ultra 3 if the display is what you stare at all day — refresh rate, brightness, or sharpness is where the difference will be most visible. The biggest gaps in its favor are peak brightness, display size, weight, among others.
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. Its strongest claims are battery life.
Both ship with comparable ecg, spo2, water resistance, so those specs don't separate the two — focus on the differences below.
Bottom line: there is no wrong answer here — match the spec advantages to how you actually use the product. The Mars Score parity tells you both are well-rounded; the differences are about trade-offs, not quality.
Why Apple - Watch Ultra 3 wins
- ▲Peak brightness — 200.00% more. 3000 nits vs 1000 nits.
- ▲Display size — 45.71% more. 2.04 " vs 1.4 ".
- ▲Weight — 11.00 g less. 62 vs 73.
- ▲Has Cellular.
Why Garmin - Fenix 8 (47mm) wins
- ▲Battery life — 433.33% more. 384 h vs 72 h.
Spec comparison
Design
| Spec | Apple - Watch Ultra 3 | Garmin - Fenix 8 (47mm) |
|---|---|---|
| Case size | 49 mmlead | 47 mm |
| Weight | 62 glead | 73 g |
| Case material | titanium | fiber-reinforced polymer |
| Water resistanceⓘ | 10 ATM | 10 ATM |
Display
| Spec | Apple - Watch Ultra 3 | Garmin - Fenix 8 (47mm) |
|---|---|---|
| Display size | 2.04 "lead | 1.4 " |
| Always-on display | true | true |
| Peak brightnessⓘ | 3000 nitslead | 1000 nits |
Health & Fitness
| Spec | Apple - Watch Ultra 3 | Garmin - Fenix 8 (47mm) |
|---|---|---|
| ECG | true | true |
| SpO2 | true | true |
| Temperature sensor | true | true |
| Sleep tracking | true | true |
| Blood pressure | false | false |
Battery & Connectivity
| Spec | Apple - Watch Ultra 3 | Garmin - Fenix 8 (47mm) |
|---|---|---|
| Battery life | 72 h | 384 hlead |
| GPS | true | true |
| Cellular | truelead | false |
| NFC | true | true |
| OS | watchOS | Garmin OSlead |
Frequently asked
Which has longer battery life, Watch Ultra 3 or Fenix 8 (47mm)?+
Fenix 8 (47mm) lasts 384h vs 72h.
Do Watch Ultra 3 or Fenix 8 (47mm) support ECG?+
Both support ECG.
Which has cellular, Watch Ultra 3 or Fenix 8 (47mm)?+
Watch Ultra 3 offers a cellular variant; Fenix 8 (47mm) is Wi-Fi only.
Spec-level deep dives
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