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MobileIQ

Head to head

Apple Apple Watch Series 12 46mmvsApple Apple Watch Ultra 3 49mm

Released
2026-09-18Apple UK Newsroom — Apple Watch Series 12, retrieved 2026-09-13
Price
£419Apple UK store — Series 12 46mm aluminium GPS, retrieved 2026-09-22
Security updates until
Not published by the makerApple UK — watchOS 27 compatible models, retrieved 2026-09-22
Released
2025-09-19Apple UK Newsroom — Apple Watch Ultra 3, retrieved 2026-09-13
Security updates until
Not published by the makerApple UK — watchOS 27 compatible models, retrieved 2026-09-22

1 win for Apple Watch Series 12 46mm1 win for Apple Watch Ultra 3 49mm2 gaps borderline0 differences you won’t notice

Verdict: Apple Watch Series 12 46mm ahead on 1 row, Apple Watch Ultra 3 49mm on 1 row

On the makers’ published figures, the Apple Watch Series 12 46mm wins on weight (case only) (39.5 g against 61.6 g); the Apple Watch Ultra 3 49mm wins on peak brightness (3,000 nits against 2,000 nits). 2 gaps are borderline, differences most people would not notice: battery life (maker's claim) (42 h against 24 h) for the Apple Watch Ultra 3 49mm and charge to 80% (30 min against 45 min) for the Apple Watch Series 12 46mm. The other 26 rows have no threshold or no direction to judge by, so nobody wins them.

True to scale

Apple Watch Series 12 46mm · 46 × 40 mmApple Watch Ultra 3 49mm · 49 × 44 mm

Case outlines from each maker’s published dimensions, drawn to scale. Corner rounding is our drawing convention, not a measurement.

Specifications

A win is marked only where the figures can be ranked and the gap is one you could notice on the wrist. A row the site has no threshold for says whether the two differ, and that it is not ranking them. = marks the same figure on both, ≠ not ranked a difference with no ranking. Every figure carries its source.

Body

SpecificationApple Watch Series 12 46mmApple Watch Ultra 3 49mm
DimensionsDiffers, but not ranked.
46 x 40 x 9.7 mmOfficial
49 x 44 x 12 mmOfficial
Case size
46mmOfficial
49mmOfficial
Case shapeSame.
rectangularOfficial
rectangularOfficial
Weight (case only)
39.5gOfficialwins this row
61.6gOfficial

Apple Watch Series 12 46mm is ahead here, by a gap you’d notice.

Case materialDiffers, but not ranked.
AluminiumOfficial
TitaniumOfficial
Water ratingDiffers, but not ranked.
Water resistance 50m (swimproof) under ISO standard 22810:2010Official
Water resistance 100m (swim, snorkel, scuba, high-speed water sports) under ISO standard 22810:2010; EN13319 recreational scuba diving to 40mOfficial

Display

SpecificationApple Watch Series 12 46mmApple Watch Ultra 3 49mm
Display typeSame.
Always-On Retina display with wide-angle OLEDs and LTPO3Official
Always-On Retina display with wide-angle OLEDs and LTPO3Official
Display areaDiffers, but not ranked.
1196mm²Official
1245mm²Official
ResolutionDiffers, but not ranked.
416 x 496Official
422 x 514Official
Peak brightness
2000nitsOfficial
3000nitsOfficialwins this row

Apple Watch Ultra 3 49mm is ahead here, by a gap you’d notice.

Always-on displaySame.
YesOfficial
YesOfficial

Platform

SpecificationApple Watch Series 12 46mmApple Watch Ultra 3 49mm
Operating systemDiffers, but not ranked.
watchOS 27Official
watchOS 26Official
ChipDiffers, but not ranked.
S11 SiPOfficial
S10 SiPOfficial
StorageSame.
64GBOfficial
64GBOfficial

Battery

SpecificationApple Watch Series 12 46mmApple Watch Ultra 3 49mm
Battery life (maker's claim)
24hOfficial
42hOfficial

Marginal — most people won’t notice.

Battery capacity
No verified data
599mAh3rd party
Charge to 80%
30minOfficial
45minOfficial

Marginal — most people won’t notice.

ChargingSame.
Fast-charge capable, Apple Watch Magnetic Fast Charger to USB-C CableOfficial
Fast-charge capable, Apple Watch Magnetic Fast Charger to USB-C CableOfficial

Health

SpecificationApple Watch Series 12 46mmApple Watch Ultra 3 49mm
SensorsDiffers, but not ranked.
Health Sensing System (third-generation electrical heart sensor, always-on optical heart sensor, blood oxygen sensor, temperature sensor), compass, always-on altimeter, high-g accelerometer, high dynamic range gyroscope, ambient light sensor, depth gauge to 6 metres, water temperature sensorOfficial
Electrical heart sensor, third-generation optical heart sensor, blood oxygen sensor, temperature sensor, depth gauge, water temperature sensor, compass, always-on altimeter, high-g accelerometer, high dynamic range gyroscope, ambient light sensorOfficial
ECGSame.
YesOfficial
YesOfficial
Blood oxygenSame.
YesOfficial
YesOfficial
Skin temperatureSame.
YesOfficial
YesOfficial
GPSDiffers, but not ranked.
Precision L1 GPS (GPS, GLONASS, Galileo, QZSS and BeiDou)Official
L1 and L5 precision dual-frequency GPS (GPS, GLONASS, Galileo, QZSS and BeiDou)Official

Connectivity

SpecificationApple Watch Series 12 46mmApple Watch Ultra 3 49mm
Cellular modelSame.
YesOfficial
YesOfficial
UK networks with eSIMDiffers, but not ranked.
EE, Vodafone, Three3rd party
EE, Vodafone, O2, Three3rd party
Wi-FiSame.
Wi-Fi 4 (802.11n)Official
Wi-Fi 4 (802.11n)Official
BluetoothSame.
5.3Official
5.3Official
NFC paymentsSame.
YesOfficial
YesOfficial

Compatibility

SpecificationApple Watch Series 12 46mmApple Watch Ultra 3 49mm
Works withDiffers, but not ranked.
iPhone 11 or later, including iPhone SE (2nd generation or later), with iOS 27 or laterOfficial
iPhone 11 or later, including iPhone SE (2nd generation or later), with iOS 26 or laterOfficial
CompatibilitySame.
iPhone onlyOfficial
iPhone onlyOfficial
5 attributes neither watch has a sourced figure for

Strap width · Display size · RAM · Blood pressure · Cellular model price. Rows appear as sources are cited — a gap in our data, not a statement about either watch.

The pairs a buyer of either watch would also weigh. Any two watches in the catalogue can be compared from the chooser.