Overview and summary
The Apple Watch Series 3 and Series 4 are generations apart in capability and experience. Series 3, released in 2017, established reliable performance and everyday fitness features. Series 4, released two years later in 2019, introduced a larger display, faster processor, advanced heart and fall detection, and a redesigned chassis. This comparison clarifies their differences in design, sensors, performance, connectivity, battery life, and software support to help you choose or understand their roles today.
Design, display, and build changes
At a glance, Series 3 and Series 4 look similar but differ in key ways. Series 4 enlarged the display by shifting the top sensor housing to the crown side and using smaller top bezels, adding more screen without increasing the case size. Series 4 also introduced a larger, flatter back glass and a softer chamfer on the edges for comfort. Series 3 has a slightly smaller screen with thicker bezels and a rear design that more closely echoes the Series 2. Both are IP68 rated, but Series 4’s front button and digital crown are designed for better water expulsion.
Size and display
Series 3 offers 38 mm and 42 mm cases, while Series 4 expanded to 40 mm and 44 mm to provide more screen area for richer complications and easier reading. The higher-resolution Series 4 display with thinner borders makes on-watch navigation and notifications clearer, which matters for users who rely on glanceable information throughout the day.
Hardware, performance, and battery
Under the hood, Series 4 brought a dual-core processor that Apple claimed was up to 70 percent faster than Series 3’s S3 chip. App launches, animations, and overall responsiveness feel smoother on Series 4, especially with more complex watch faces and complication setups. Both watches support workout auto-detection and background app refresh, but Series 4 handles more concurrent tasks and future software updates better. Battery life is comparable in typical use, with both offering around 18 hours, though Series 4’s larger display and faster chip balance efficiency with higher performance demands.
Performance snapshot
| Metric | Apple Watch Series 3 | Apple Watch Series 4 | Source/Notes |
|---|---|---|---|
| Processor | S3 SiP with M9 motion coprocessor | S4 SiP with M10 motion coprocessor | Apple tech specs and teardowns |
| Display size options | 38 mm, 42 mm | 40 mm, 44 mm | Apple product pages |
| Typical battery life | ~18 hours | ~18 hours | Apple estimates; real-world varies with usage |
| Water resistance | IP68 (50 m) | IP68 (50 m) | Certification unchanged, improved chassis design |
Sensors and health features
Health and sensor upgrades are the most meaningful differentiators. Series 4 added an electrical heart sensor for single-lead ECG app readings, a new optical heart sensor enabling noisy IR-based readings for better accuracy, and an accelerometer and gyroscope tuned for fall detection. Series 3 includes the original optical heart sensor and third-generation accelerometer, suitable for workouts and general activity, but lacks ECG and the enhanced fall detection algorithms. Both track heart rate during workouts, but Series 4’s hardware supports more detailed readings and at-rest heart rate insights.
Health feature comparison
| Feature | Series 3 | Series 4 | Notes |
|---|---|---|---|
| Heart sensor (photometric) | Yes | Yes | Both measure heart rate and HRV |
| Electrical heart sensor / ECG | No | Yes | Series 4 only; requires supported regions |
| Fall detection | No | Yes | Series 4 only; uses accelerometer and algorithms |
| Noise-approximate IR heart readings |
Connectivity, GPS, and LTE
Both models include built-in GPS and Wi‑Fi b/g/n, with Bluetooth 4.2 and support for 802.11 networks. Series 4 added dual‑band Wi‑Fi (802.11a/b/g/n/ac) for faster local networks and, in cellular variants, support for additional LTE bands, improving connectivity and speeds where available. For users who rely on on‑watch streaming or notifications when the iPhone is distant, Series 4’s improved radios and LTE compatibility are practical advantages. Series 3 remains capable for calls and data when paired closely, but LTE support is limited to earlier bands.
Connectivity summary
- Both: Bluetooth 4.2, Wi‑Fi b/g/n, GPS
- Series 4: Dual‑band Wi‑Fi, more LTE bands, faster fallbacks to 3G/2G
- Series 3: Good for everyday pairing, but fewer network options
Software, compatibility, and longevity
Both watches receive ongoing watchOS updates, but Series 4 tends to receive new features and optimizations longer due to its more capable hardware. As of the latest watchOS versions available through the support window, Series 4 typically gains features such as noise level, ECG app extensions, and additional workout metrics earlier or exclusively. App compatibility leans toward Series 4 over time as developers target newer silicon and sensors. If you rely on specific apps or want longer software support, Series 4 holds an advantage, though Series 3 remains functional for fitness tracking and basic notifications.
Pricing, value, and who should buy which
Today, Series 3 models are available at significantly lower prices, often attractive to first-time buyers or secondary wearables. Series 4 models command a premium for their larger screen, extra sensors, and improved performance. If your priorities are basic timekeeping and activity tracking and you are budget-constrained, Series 3 offers solid value. If you want ECG, fall detection, a larger display, faster performance, and longer software relevance, Series 4 is the safer investment. Consider also that Series 4 remains more compatible with newer watchOS features and a broader range of third‑party apps.
Conclusion and recommendation
Choose Apple Watch Series 4 if you want the best balance of display size, health capabilities, performance, and future-proofing. Opt for Series 3 only if budget is a firm constraint and your needs are limited to core fitness tracking and timekeeping. For most users prioritizing longevity and feature completeness, Series 4 remains the more durable and capable option in this evergreen comparison.