Where they actually differ
The most decisive specs, ranked by how much they matter — before the full spec table.
| Spec | Samsung - Galaxy Watch 7 (40mm) | OnePlus Watch 3 |
|---|---|---|
| Battery life | 30 h | 120 h |
| Weight | 28.8 g | 81 g |
| Peak brightness | 3000 nits | 2200 nits |
| Display size | 1.31 " | 1.5 " |
| Cellular | true | false |
Between the Galaxy Watch 7 (40mm) and OnePlus Watch 3, the Galaxy Watch 7 (40mm) comes out ahead in weight / peak brightness, while the OnePlus Watch 3 wins on battery life / display size. Overall, the Galaxy Watch 7 (40mm) scores 69.6 and the OnePlus Watch 3 scores 65.7 on our Mars Score.
Which should you buy?
The Galaxy Watch 7 (40mm) edges ahead on the Mars Score (69.6 vs 65.7), but the 3.9-point gap is small enough that the right pick comes down to which spec advantages matter to you.
Pick the Galaxy Watch 7 (40mm) 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 weight, peak brightness, cellular. The single most decisive one: Weight — 52.20 g less. 28.8 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, display size. The single most decisive one: Battery life — 300.00% more. 120 h vs 30 h.
Both ship with comparable ecg, spo2, water resistance, 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: Samsung - Galaxy Watch 7 (40mm) or OnePlus Watch 3?
Samsung - Galaxy Watch 7 (40mm) leads the current Mars Score by 3.9 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 Samsung - Galaxy Watch 7 (40mm) if…
Samsung - Galaxy Watch 7 (40mm) has the measurable edge on weight g, peak brightness nits, has cellular.
Choose OnePlus Watch 3 if…
OnePlus Watch 3 has the measurable edge on battery life h, display size in.
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 Samsung - Galaxy Watch 7 (40mm) wins
- ▲Weight — 52.20 g less. 28.8 vs 81.
- ▲Peak brightness — 36.36% more. 3000 nits vs 2200 nits.
- ▲Has Cellular.
Why OnePlus Watch 3 wins
- ▲Battery life — 300.00% more. 120 h vs 30 h.
- ▲Display size — 14.50% more. 1.5 " vs 1.31 ".
Spec comparison
Design
| Spec | Samsung - Galaxy Watch 7 (40mm) | OnePlus Watch 3 |
|---|---|---|
| Case size | 40 mm | 46.5 mmlead |
| Weight | 28.8 glead | 81 g |
| Case material | aluminum | stainless steel |
| Water resistanceⓘ | 5 ATM | 5 ATM |
Display
| Spec | Samsung - Galaxy Watch 7 (40mm) | OnePlus Watch 3 |
|---|---|---|
| Display size | 1.31 " | 1.5 "lead |
| Always-on display | true | true |
| Peak brightnessⓘ | 3000 nitslead | 2200 nits |
Health & Fitness
| Spec | Samsung - Galaxy Watch 7 (40mm) | OnePlus Watch 3 |
|---|---|---|
| ECG | true | true |
| SpO2 | true | true |
| Temperature sensor | true | true |
| Sleep tracking | true | true |
| Blood pressure | truelead | false |
Battery & Connectivity
| Spec | Samsung - Galaxy Watch 7 (40mm) | OnePlus Watch 3 |
|---|---|---|
| Battery lifeⓘ | 30 h | 120 hlead |
| GPS | true | true |
| Cellular | truelead | false |
| NFC | true | true |
| OS | WearOS | WearOS |
Frequently asked
Which has longer battery life, Galaxy Watch 7 (40mm) or OnePlus Watch 3?+
OnePlus Watch 3 lasts 120 hours vs 30 hours.
Do Galaxy Watch 7 (40mm) or OnePlus Watch 3 support ECG?+
Both support ECG.
Which has cellular, Galaxy Watch 7 (40mm) or OnePlus Watch 3?+
Galaxy Watch 7 (40mm) offers a cellular variant; OnePlus Watch 3 is Wi-Fi only.