Where they actually differ
The most decisive specs, ranked by how much they matter — before the full spec table.
| Spec | Amazfit - T-Rex 3 | Samsung - Galaxy Watch 7 (40mm) |
|---|---|---|
| Battery life | 672 h | 30 h |
| Peak brightness | 2000 nits | 3000 nits |
| Weight | 68 g | 28.8 g |
| Display size | 1.5 " | 1.31 " |
| Water resistance | 10 ATM | 5 ATM |
| ECG | false | true |
Between the T-Rex 3 and Galaxy Watch 7 (40mm), the T-Rex 3 comes out ahead in battery life / display size, while the Galaxy Watch 7 (40mm) wins on peak brightness / weight. Overall, the T-Rex 3 scores 62.7 and the Galaxy Watch 7 (40mm) scores 69.6 on our Mars Score.
Which should you buy?
The Galaxy Watch 7 (40mm) edges ahead on the Mars Score (62.7 vs 69.6), but the 6.9-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, display size, water resistance. The single most decisive one: Battery life — 2140.00% more. 672 h vs 30 h.
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. Its strongest claims are peak brightness, weight, ecg, among others. The single most decisive one: Peak brightness — 50.00% more. 3000 nits vs 2000 nits.
Both ship with comparable spo2, so those specs do not separate the two — focus on the differences below.
Bottom line: the Galaxy Watch 7 (40mm) 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: Amazfit - T-Rex 3 or Samsung - Galaxy Watch 7 (40mm)?
Samsung - Galaxy Watch 7 (40mm) leads the current Mars Score by 6.9 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 Amazfit - T-Rex 3 if…
Amazfit - T-Rex 3 has the measurable edge on battery life h, display size in, water resistance atm.
Choose Samsung - Galaxy Watch 7 (40mm) if…
Samsung - Galaxy Watch 7 (40mm) has the measurable edge on peak brightness nits, weight g, 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 — 2140.00% more. 672 h vs 30 h.
- ▲Display size — 14.50% more. 1.5 " vs 1.31 ".
- ▲Water resistance — 5.00 ATM more. 10 vs 5.
Why Samsung - Galaxy Watch 7 (40mm) wins
- ▲Peak brightness — 50.00% more. 3000 nits vs 2000 nits.
- ▲Weight — 39.20 g less. 28.8 vs 68.
- ▲Has ECG.
- ▲Has Cellular.
Spec comparison
Design
| Spec | Amazfit - T-Rex 3 | Samsung - Galaxy Watch 7 (40mm) |
|---|---|---|
| Case size | 48.5 mmlead | 40 mm |
| Weight | 68 g | 28.8 glead |
| Case material | polymer | aluminum |
| Water resistanceⓘ | 10 ATMlead | 5 ATM |
Display
| Spec | Amazfit - T-Rex 3 | Samsung - Galaxy Watch 7 (40mm) |
|---|---|---|
| Display size | 1.5 "lead | 1.31 " |
| Always-on display | true | true |
| Peak brightnessⓘ | 2000 nits | 3000 nitslead |
Health & Fitness
| Spec | Amazfit - T-Rex 3 | Samsung - Galaxy Watch 7 (40mm) |
|---|---|---|
| ECG | false | truelead |
| SpO2 | true | true |
| Temperature sensor | true | true |
| Sleep tracking | true | true |
| Blood pressure | false | truelead |
Battery & Connectivity
| Spec | Amazfit - T-Rex 3 | Samsung - Galaxy Watch 7 (40mm) |
|---|---|---|
| Battery lifeⓘ | 672 hlead | 30 h |
| GPS | true | true |
| Cellular | false | truelead |
| NFC | false | truelead |
| OS | Zepp OSlead | WearOS |
Frequently asked
Which has longer battery life, T-Rex 3 or Galaxy Watch 7 (40mm)?+
T-Rex 3 lasts 672 hours vs 30 hours.
Do T-Rex 3 or Galaxy Watch 7 (40mm) support ECG?+
Galaxy Watch 7 (40mm) supports ECG; T-Rex 3 does not.
Which has cellular, T-Rex 3 or Galaxy Watch 7 (40mm)?+
Galaxy Watch 7 (40mm) offers a cellular variant; T-Rex 3 is Wi-Fi only.