Where they actually differ
The most decisive specs, ranked by how much they matter — before the full spec table.
| Spec | Amazfit - T-Rex 3 | OnePlus Watch 3 |
|---|---|---|
| Battery life | 672 h | 120 h |
| Weight | 68 g | 81 g |
| Peak brightness | 2000 nits | 2200 nits |
| Water resistance | 10 ATM | 5 ATM |
| ECG | false | true |
Between the T-Rex 3 and OnePlus Watch 3, the T-Rex 3 comes out ahead in battery life / weight, while the OnePlus Watch 3 wins on peak brightness / ecg. Overall, the T-Rex 3 scores 62.7 and the OnePlus Watch 3 scores 65.7 on our Mars Score.
Which should you buy?
The OnePlus Watch 3 edges ahead on the Mars Score (62.7 vs 65.7), but the 3.0-point gap is small enough that the right pick comes down to which spec advantages matter to you.
Pick the T-Rex 3 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. The single most decisive one: Battery life — 460.00% more. 672 h vs 120 h.
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, ecg. The single most decisive one: Peak brightness — 10.00% more. 2200 nits vs 2000 nits.
Both ship with comparable display size, cellular, spo2, so those specs do not 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 says both are well-rounded; the differences are about trade-offs, not quality.
Which should you buy: Amazfit - T-Rex 3 or OnePlus Watch 3?
OnePlus Watch 3 leads the current Mars Score by 3.0 points.The more useful decision is the trade-off behind that result: compare battery life against the way you will actually use the product.
Choose Amazfit - T-Rex 3 if…
Amazfit - T-Rex 3 has the measurable edge on battery life h, weight g, water resistance atm.
Choose OnePlus Watch 3 if…
OnePlus Watch 3 has the measurable edge on peak brightness nits, has ecg.
This is a structured comparison of the published catalog values. It is not a claim of identical real-world performance across every workload; use the linked spec drill-downs and methodology page to inspect the inputs.
Why Amazfit - T-Rex 3 wins
- ▲Battery life — 460.00% more. 672 h vs 120 h.
- ▲Weight — 13.00 g less. 68 vs 81.
- ▲Water resistance — 5.00 ATM more. 10 vs 5.
Why OnePlus Watch 3 wins
- ▲Peak brightness — 10.00% more. 2200 nits vs 2000 nits.
- ▲Has ECG.
Spec comparison
Design
| Spec | Amazfit - T-Rex 3 | OnePlus Watch 3 |
|---|---|---|
| Case size | 48.5 mmlead | 46.5 mm |
| Weight | 68 glead | 81 g |
| Case material | polymer | stainless steel |
| Water resistanceⓘ | 10 ATMlead | 5 ATM |
Display
| Spec | Amazfit - T-Rex 3 | OnePlus Watch 3 |
|---|---|---|
| Display size | 1.5 " | 1.5 " |
| Always-on display | true | true |
| Peak brightnessⓘ | 2000 nits | 2200 nitslead |
Health & Fitness
| Spec | Amazfit - T-Rex 3 | OnePlus Watch 3 |
|---|---|---|
| ECG | false | truelead |
| SpO2 | true | true |
| Temperature sensor | true | true |
| Sleep tracking | true | true |
| Blood pressure | false | false |
Battery & Connectivity
| Spec | Amazfit - T-Rex 3 | OnePlus Watch 3 |
|---|---|---|
| Battery lifeⓘ | 672 hlead | 120 h |
| GPS | true | true |
| Cellular | false | false |
| NFC | false | truelead |
| OS | Zepp OSlead | WearOS |
Frequently asked
Which has longer battery life, T-Rex 3 or OnePlus Watch 3?+
T-Rex 3 lasts 672 hours vs 120 hours.
Do T-Rex 3 or OnePlus Watch 3 support ECG?+
OnePlus Watch 3 supports ECG; T-Rex 3 does not.
Which has cellular, T-Rex 3 or OnePlus Watch 3?+
Neither offers cellular.