Comparison · Fitness watches · Desk research
Apple Watch Series 4 vs Apple Watch Ultra 4
Quick Answer
Series 4 (2018) is the first Apple Watch with an electrical heart sensor and the ECG app; Apple Support still lists the S4 SiP, 16GB, 40mm or 44mm cases, an LTPO OLED with Force Touch (not Always-On), 1000 nits, and up to 18 hours from an August 2018 test. Ultra 4 (announced 9 September 2026) is a different product: 49mm Grade 5 titanium, S11 with 64GB, Always-On LTPO3 at 3,000 nits, dual-frequency GPS, Action Button, 100m / EN 13319 40m.
The verdict
Apple Watch Series 4 or Apple Watch Ultra 4 — quote the two manufacturer sheets.
Why: This is an eight-year hardware jump. Series 4 is the 40/44mm ECG-debut watch with Force Touch (no Always-On), 16GB, and Apple’s August 2018 18-hour test. Ultra 4 is the current 49mm adventure SKU on watchOS 27. Apple’s Series 12 Newsroom list for watchOS 27 starts at Series 9 / SE 3 / Ultra 2 — Series 4 is not on that list. Quote Apple’s list; this page does not invent an end-of-support date.
Buy Apple Watch Series 4 if
You already wear Series 4, ECG plus 50m swimproof still covers what you do, and you are not shopping for watchOS 27, Always-On, satellite, or a 40m dive path.
Buy Apple Watch Ultra 4 if
You want Apple’s current 49mm adventure watch: Grade 5 titanium, Action Button, dual-frequency GPS, satellite SOS/Messages/Find My, Health Sensing System, and Apple’s 50-hour normal-use / 45-hour Max Extended Workout claims.
Spec comparison
OEM rows only. Series 4 numbers are from Apple Support 111984 (and the 12 September 2018 Newsroom post where the Support page is silent). Ultra 4 numbers are from apple.com/apple-watch-ultra-4/specs/. Cells Apple does not publish stay marked.
| Spec | Series 4 | Ultra 4 |
|---|---|---|
| Year introduced (Support / Newsroom) | 2018 (Newsroom 12 September 2018) | 2026 (Newsroom 9 September 2026) |
| Case size(s) | 40mm and 44mm | 49mm only |
| Case material | Aluminum or stainless steel (Hermès SS; Nike+ aluminum) | Grade 5 titanium |
| Dimensions (44mm Al / 49mm) | 44 × 38 × 10.7mm | 49 × 44 × 12mm |
| Display | LTPO OLED Retina with Force Touch; 40mm 324×394; 44mm 368×448; 1000 nits. Always-On not listed | Always-On LTPO3; 422×514; 326 ppi; 3,000 nits peak; 1 nit minimum |
| Chip / storage | S4 with 64-bit dual-core processor; 16GB | S11; 64GB |
| Battery — normal use | Up to 18 hours (Apple test, August 2018) | Up to 50 hours |
| Battery — Low Power / extra modes | Not listed on Support 111984 | Up to 84 hours Low Power; 18 hours outdoor; 25 hours Extended; 45 hours Max Extended Workout |
| Fast charge (OEM) | Magnetic charging cable; no 15-minute / 80% figures on Support 111984 | ~80% in about 45 minutes; 15 min ≈ 18 hours normal use |
| Weight (example SKUs) | Al 40mm 30.1g; Al 44mm 36.7g; SS 40mm 39.8g; SS 44mm 47.9g | 63.0g natural titanium; 63.1g black titanium (case only) |
| Wireless | Bluetooth 5.0; Wi-Fi 802.11b/g/n 2.4GHz | Bluetooth 5.3; Wi-Fi 4 (802.11n) 2.4GHz and 5GHz |
| GNSS | GPS, GLONASS, Galileo, and QZSS (no dual-frequency row) | Precision dual-frequency GPS |
| Water | 50m (ISO 22810:2010); Apple: pool/ocean swim, not scuba or high-velocity water | 100m (ISO 22810:2010); EN 13319 recreational dive to 40m |
| Dust / MIL | Not listed | IP6X; MIL-STD-810H subsection list |
| Action Button / siren | Not listed | Action Button; siren Apple says is audible to 180m / 600 feet |
| Satellite | Not listed | Emergency SOS, Messages, Find My via satellite |
| Heart rate | Electrical heart sensor; optical heart sensor | Health Sensing System |
| ECG / Blood Oxygen | ECG app (Newsroom 2018; Ultra 4 footnote: Series 4+, excluding SE). Blood Oxygen not on Support 111984 | ECG app; Blood Oxygen app (region limits) |
| OS / phone | Original Support pairing: iPhone 6 or later + iOS 12 (cellular); iPhone 5s or later + iOS 12 (GPS). Do not invent current pairing | watchOS 27; iPhone 11 or later / SE 2+, iOS 27 |
| watchOS 27 (Apple list) | Not named on the Series 12 Newsroom list | On the list (Ultra 2 or later) |
| US start (dated) | Discontinued; no street price treated as fact here | $799 (Newsroom, 9 September 2026) |
Who each watch is for
Series 4 is the 2018 everyday Apple Watch that introduced ECG on the wrist. If it still runs the software you already have, and you do not need Always-On, dual-frequency GNSS, satellite, or a dive computer path, Apple’s listed 2018 feature set is the whole story.
Ultra 4 is the current adventure Apple Watch. The comparison is not “slightly brighter Series.” It is a 49mm titanium case, S11, Health Sensing System, and the 50 / 84 / 45-hour OEM table versus a 40/44mm Force Touch watch with 16GB and an 18-hour August 2018 test note.
watchOS 27 — quote Apple
Series 12 Newsroom, 9 September 2026: “watchOS 27 will be available for Apple Watch Series 9 or later, Apple Watch SE 3, and Apple Watch Ultra 2 or later on Monday, September 14, and requires iPhone 11 or later or iPhone SE (2nd generation or later) with iOS 27 or later.” Series 4 is not on that sentence. This page does not invent an end-of-support date.
Display and storage
Series 4 Support: Force Touch LTPO OLED, 1000 nits, 324×394 (40mm) / 368×448 (44mm), 16GB. Ultra 4: Always-On LTPO3, 422×514, 3,000 nits peak, 64GB. Do not write Always-On onto Series 4.
Battery
Copy Apple’s mode names. Series 4: up to 18 hours; testing conducted by Apple in August 2018 using preproduction GPS and GPS + Cellular units (Support footnote 3). Ultra 4: 50 / 84 / 18 / 25 / 45 hours; 15 minutes → up to 18 hours. Max Extended Workout is outdoor run/walk/hike with GPS every second — not a published triathlon or dive number.
GNSS, water, and satellite
Series 4 is single-band GPS with GLONASS, Galileo, and QZSS, and 50m swimproof as Apple worded ISO 22810:2010 (not scuba). Ultra 4 is dual-frequency GNSS, 100m / 40m dive, Action Button, and satellite. Do not upgrade Series 4 to “Ultra GPS” in prose.
Price
Ultra 4 starts at $799 (US) on Apple Newsroom, 9 September 2026. Series 4 is discontinued; Apple Support is the spec source. This page does not treat a refurb or classifieds number as a fact.
Frequently asked questions
Does Series 4 get watchOS 27?
Apple’s Series 12 Newsroom (9 September 2026) says watchOS 27 will be available for Apple Watch Series 9 or later, Apple Watch SE 3, and Apple Watch Ultra 2 or later, and requires iPhone 11 or later or iPhone SE (2nd generation or later) with iOS 27 or later. Series 4 is not on that list. This page quotes Apple.
Did Series 4 introduce ECG?
Yes, as Apple’s 12 September 2018 Newsroom describes it: Series 4 added an electrical heart rate sensor that can take an electrocardiogram using the ECG app (FDA De Novo classification in that launch copy). Apple’s Ultra 4 spec-sheet footnote still states the ECG app is available on Series 4 and later, excluding Apple Watch SE models. ECG remains region- and age-gated.
Is Series 4 Always-On?
No. Series 4 Support lists an LTPO OLED Retina display with Force Touch at 1000 nits. Always-On is not on that spec sheet. Always-On debuted on Series 5 (Apple Newsroom, 10 September 2019; Support 118453).
Does Series 4 have satellite, an Action Button, or a 40m dive path?
No. Series 4 Support lists GPS/GLONASS/Galileo/QZSS, 50m water resistance under ISO 22810:2010, and no Action Button or satellite row. Ultra 4’s spec sheet lists precision dual-frequency GPS, Action Button, Emergency SOS / Messages / Find My via satellite, 100m water resistance, and EN 13319 recreational scuba to 40m.
What iPhone did Series 4 require?
As printed on Support 111984: Apple Watch Series 4 (GPS + Cellular) requires an iPhone 6 or later with iOS 12 or later; GPS models require an iPhone 5s or later with iOS 12 or later. That is the original requirement on the Support page. This article does not invent a current pairing list.