Where they actually differ
The most decisive specs, ranked by how much they matter — before the full spec table.
| Spec | Apple - Watch SE (2nd gen) | OnePlus Watch 3 |
|---|---|---|
| Battery life | 18 h | 120 h |
| Peak brightness | 1000 nits | 2200 nits |
| Weight | 33 g | 81 g |
| Display size | 1.78 " | 1.5 " |
| Cellular | true | false |
| ECG | false | true |
Between the Watch SE (2nd gen) and OnePlus Watch 3, the Watch SE (2nd gen) comes out ahead in weight / display size, while the OnePlus Watch 3 wins on battery life / peak brightness. Overall, the Watch SE (2nd gen) scores 55.9 and the OnePlus Watch 3 scores 65.7 on our Mars Score.
Which should you buy?
The OnePlus Watch 3 is the clear pick on raw spec strength, leading by 9.8 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 Watch SE (2nd gen) if you carry the device everywhere and weight or thickness has been the deciding factor before. The biggest gaps in its favor are weight, display size, cellular. The single most decisive one: Weight — 48.00 g less. 33 vs 81.
Pick the OnePlus Watch 3 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, peak brightness, ecg, among others. The single most decisive one: Battery life — 566.67% more. 120 h vs 18 h.
Both ship with comparable water resistance, so those specs do not separate the two — focus on the differences below.
Bottom line: the OnePlus Watch 3 is the safer default. The other model is the right choice only when its specific advantages line up with your priorities.
Which should you buy: Apple - Watch SE (2nd gen) or OnePlus Watch 3?
OnePlus Watch 3 leads the current Mars Score by 9.8 points.The more useful decision is the trade-off behind that result: compare display size, battery life against the way you will actually use the product.
Choose Apple - Watch SE (2nd gen) if…
Apple - Watch SE (2nd gen) has the measurable edge on weight g, display size in, has cellular.
Choose OnePlus Watch 3 if…
OnePlus Watch 3 has the measurable edge on battery life h, 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 Apple - Watch SE (2nd gen) wins
- ▲Weight — 48.00 g less. 33 vs 81.
- ▲Display size — 18.67% more. 1.78 " vs 1.5 ".
- ▲Has Cellular.
Why OnePlus Watch 3 wins
- ▲Battery life — 566.67% more. 120 h vs 18 h.
- ▲Peak brightness — 120.00% more. 2200 nits vs 1000 nits.
- ▲Has ECG.
- ▲Has SpO2.
Spec comparison
Design
| Spec | Apple - Watch SE (2nd gen) | OnePlus Watch 3 |
|---|---|---|
| Case size | 44 mm | 46.5 mmlead |
| Weight | 33 glead | 81 g |
| Case material | aluminum | stainless steel |
| Water resistanceⓘ | 5 ATM | 5 ATM |
Display
| Spec | Apple - Watch SE (2nd gen) | OnePlus Watch 3 |
|---|---|---|
| Display size | 1.78 "lead | 1.5 " |
| Always-on display | false | truelead |
| Peak brightnessⓘ | 1000 nits | 2200 nitslead |
Health & Fitness
| Spec | Apple - Watch SE (2nd gen) | OnePlus Watch 3 |
|---|---|---|
| ECG | false | truelead |
| SpO2 | false | truelead |
| Temperature sensor | false | truelead |
| Sleep tracking | true | true |
| Blood pressure | false | false |
Battery & Connectivity
| Spec | Apple - Watch SE (2nd gen) | OnePlus Watch 3 |
|---|---|---|
| Battery lifeⓘ | 18 h | 120 hlead |
| GPS | true | true |
| Cellular | truelead | false |
| NFC | true | true |
| OS | watchOS | WearOSlead |
Frequently asked
Which has longer battery life, Watch SE (2nd gen) or OnePlus Watch 3?+
OnePlus Watch 3 lasts 120 hours vs 18 hours.
Do Watch SE (2nd gen) or OnePlus Watch 3 support ECG?+
OnePlus Watch 3 supports ECG; Watch SE (2nd gen) does not.
Which has cellular, Watch SE (2nd gen) or OnePlus Watch 3?+
Watch SE (2nd gen) offers a cellular variant; OnePlus Watch 3 is Wi-Fi only.