Only the differences are shown. 19 specs stay the same.
+4you gain
−0you give up
Apple Watch Series 3 came out in September 2017. Apple Watch Series 4 came out in September 2018, 1 year later. Apple Watch Series 3 stopped getting new watchOS versions at watchOS 8.8.2. Apple Watch Series 4 stopped getting new watchOS versions at watchOS 10.6.2.
Note on Apple Watch Series 3: Apple lists 8GB of storage for the GPS model and 16GB for the GPS + Cellular model. The stainless steel, Hermès and Edition (ceramic) cases came only as GPS + Cellular. Apple's tech specs say "Optical heart sensor" and give no generation. The newest watchOS 8 release Apple lists is watchOS 8.8.2 (March 24, 2026).
Note on Apple Watch Series 4: Aluminum and stainless steel models are vintage; Nike+ and Hermès models are obsolete on Apple's list. watchOS 10.6.2 (Feb 2, 2026) is the newest watchOS version Apple lists for this model. Apple's compare page calls the sensor a "Second-generation optical heart sensor"; the tech specs say only "Optical heart sensor".
Updates & compatibility
watchOS 8.8.2 → watchOS 10.6.2
Varies by version — see Apple's list, S4, 16 GB storage
Display
OLED → LTPO OLED
The only change here
Health sensors
Optical heart sensor → Second-generation optical heart sensor
ECG
Design & durability
38 mm, 42 mm → 40 mm, 44 mm
Aluminum, stainless steel, 30.1–47.9 g
Price check
Series 4 launched at $399
Not currently sold refurbished by Back Market or Apple.
Updates & compatibility1 gain · 4 changes
Latest watchOS
watchOS 8.8.2›watchOS 10.6.2
What does this mean?
watchOS is the software that runs Apple Watch: the watch faces, the built-in apps and the settings. A new version can bring redesigned apps, new watch faces and new workout features.
To install a new watchOS, the paired iPhone needs a matching iOS: watchOS 27 needs iPhone 11 or later, or iPhone SE (2nd generation or later), with iOS 27. If the watch cannot run the newest version, Software Update offers the newest one it can use. After watchOS 11 came watchOS 26, so watchOS 11 to watchOS 27 is two updates, not sixteen.
Matters most if: You are buying a used Apple Watch, or your iPhone is too old for the latest iOS.
Last security update
watchOS 8.8.2 on March 24, 2026›watchOS 10.6.2 on February 2, 2026
watchOS 8.8.2: maintenance update (no published security fixes). watchOS 10.6.2: maintenance update (no published security fixes). Apple Watch Series 3 and Apple Watch Series 4 can't run watchOS 27. Apple says not all known security issues are fixed in older versions. Apple's note on software updates
What does this mean?
The most recent update Apple has released for the newest watchOS version this Apple Watch can run, and the day it came out, from Apple's list of security releases.
Apple's list says which updates fixed security problems. A maintenance update fixed other things and lists no security fixes. Apple says not all known security issues are fixed in older watchOS versions, even ones that still get updates.
Matters most if: You are buying a used Apple Watch, or you use Apple Pay on it.
Apple repair support
Vintage: limited repairs›Varies by version — see Apple's list
What does this mean?
Apple counts from when it stopped selling the model, not from its release date. Vintage: Apple stopped selling it 5 to 7 years ago; repairs only while parts last. Obsolete: over 7 years ago; Apple no longer repairs it.
Checked against Apple's vintage and obsolete products list on 2026-10-11.
Chip
S3›S4
What does this mean?
The chip is the watch's brain. Apple names its watch chips S1, S2 and so on; the newest is the S11.
The chip decides which features a watch can get. Double tap and on-device Siri arrived with the S9 chip in Series 9 and Ultra 2: double tap uses the chip's Neural Engine, which Apple says processes machine learning tasks. Apple said the S6 chip in Series 6 let apps launch 20 percent faster.
Storage
8 GB (GPS), 16 GB (GPS + Cellular)›16 GB
What does this mean?
The space on the watch for apps, music, podcasts, audiobooks and photos. GB means gigabytes. Apple Watch models have from 8 GB to 64 GB.
Storage matters most if you keep music, podcasts or audiobooks on the watch to play when your iPhone is not with you. On Series 3, the GPS + Cellular version has 16 GB and the GPS version 8 GB.
Matters most if: You want to listen to music or podcasts on runs or walks without your iPhone.
Double tap gesture
No (same on both)
What does this mean?
Tap the index finger and thumb of the hand wearing the watch together twice. The watch treats it like pressing the main button on the screen, so you can control it with one hand.
Answer or end a call, stop a timer, play or pause music, snooze an alarm, or scroll through the Smart Stack of widgets. It does not work in Low Power Mode, during Sleep Focus, when your wrist is down or when the watch is locked.
Matters most if: Your other hand is often busy.
On-device Siri
No (same on both)
What does this mean?
The watch can handle some Siri requests on the watch itself.
Apple says requests that need no information from the internet, such as starting a workout or setting a timer, work without Wi-Fi or cellular, and the answers come quicker. Apple added it with Series 9 and Ultra 2.
Matters most if: You use Siri for timers and workouts, or you often go out without your iPhone.
Price1 change
Price check
Apple Watch Series 4 — launched at $399
- Used on eBay
- Back Market does not list models this old
- Apple does not currently sell this model refurbished
What your Apple Watch Series 3 sells for
- Apple Trade In estimate
- Sold listings on eBay
eBay may ask you to sign in to see sold prices.
Links open in a new tab. Prices are set by each seller and change daily.
Launch price (US)
$329›$399+$70
What does this mean?
The price Apple charged in the US on launch day for the cheapest version, before tax.
This is not what it costs today. Older models drop in price over time, so check the used and refurbished links for current prices.
Display1 gain
Display type
OLED›LTPO OLED
What does this mean?
The type of screen. Apple lists an OLED screen for Series 1 and later. LTPO (low-temperature polysilicon and oxide) is a display technology Apple lists from Series 4 on, and one of the parts Apple named for the always-on screen of Series 5. LTPO2 and LTPO3 are the later versions in Apple's tech specs.
LTPO3 with wide-angle OLED is on Series 10 and later and Ultra 3 and later. Apple says Series 10's screen is up to 40 percent brighter than Series 9's when viewed from an angle, and that in always-on mode it updates once a second instead of once a minute, so some watch faces show a ticking seconds hand without you raising your wrist.
Matters most if: You want to read the watch at a glance without lifting your wrist.
Always-On display
No (same on both)
What does this mean?
The watch face and the time stay visible when your wrist is down, instead of the screen going dark.
You can see the time, and your numbers during a workout, without raising your wrist. The screen dims while your wrist is down and goes back to full brightness when you raise it. It is not available in Low Power Mode.
Peak brightness
1000 nits (same on both)
What does this mean?
Nits measure screen brightness. This is Apple's figure for the brightest the screen can get. Apple Watch screens range from 450 nits to 3000 nits.
A higher number makes the screen easier to read outdoors in strong sun. Apple says Series 9 doubled the top brightness to 2000 nits, from 1000 on Series 8. Ultra 2 reached 3000 nits.
Matters most if: You spend a lot of time outdoors, for example running or hiking.
Health sensors1 gain · 1 change
Heart rate sensor
Optical heart sensor›Second-generation optical heart sensor
What does this mean?
The optical heart sensor on the back of the watch flashes green lights against your wrist. Blood absorbs green light and more blood flows with each heartbeat, so the watch can count your heart rate in beats per minute (BPM).
The Heart Rate app shows your heart rate at rest, while walking and during and after a workout, and you can turn on alerts for a heart rate that stays above or below a level you choose. We show Apple's name for the sensor; Apple's tech specs do not say what changed between generations. Series 12 and Ultra 4 have what Apple calls the Health Sensing System, which measures heart rate as often as every 5 seconds during the day.
Matters most if: You train by heart rate, or want an alert when your heart rate stays above or below a level you set.
ECG app (electrical heart sensor)
GainAvailability varies by country. Apple's feature availability page
What does this mean?
ECG stands for electrocardiogram: a recording of the electrical signals that make your heart beat. The ECG app records one in 30 seconds while you hold a finger on the Digital Crown.
The app checks the recording for atrial fibrillation (AFib), a form of irregular heart rhythm, and saves it in the Health app, where you can export a PDF for your doctor. Apple says the app cannot detect a heart attack, blood clots or a stroke, and is not intended for people under 22. No Apple Watch SE model has it.
Matters most if: You want to record your heart rhythm on the spot, for example when you feel a rapid or skipped heartbeat.
Blood Oxygen app
No (same on both)
What does this mean?
Blood oxygen is the percentage of oxygen your red blood cells carry from your lungs to the rest of your body. The Blood Oxygen app measures it with a red light against your wrist; a reading takes 15 seconds while you keep your arm still.
With background measurements on, the watch also measures now and then, usually when you are not moving. Apple says the readings are not intended for medical use and are only for general fitness and wellness, and the app is for people 18 and older. No Apple Watch SE model has it.
Matters most if: You want to follow your blood oxygen overnight or at high elevation.
Temperature sensing
No (same on both)
What does this mean?
Two temperature sensors, one on the back near your skin and one under the display, check your wrist temperature every five seconds while you sleep.
After about 5 nights, the Health app shows each night's change from your usual temperature. It is not a thermometer: you cannot check your temperature on demand. If you use Cycle Tracking, it is also used for period predictions. Apple says it is not intended for medical purposes.
Matters most if: You use Cycle Tracking, or want to see night-to-night changes in your body temperature.
Sleep apnea notifications
No (same on both)
What does this mean?
Apple describes sleep apnea as a potentially serious condition where breathing stops repeatedly during sleep. The watch uses its motion sensor to pick up small wrist movements linked to interruptions in normal breathing.
Wear the watch to bed. If nights with more breathing disturbances become frequent over 30 days, you get a notification of possible sleep apnea, with a PDF to discuss with your healthcare provider. Apple says it is not intended for people already diagnosed with sleep apnea or under 18.
Hypertension notifications
No (same on both)
What does this mean?
Hypertension is chronic high blood pressure. The watch uses its optical heart sensor to analyze how your blood vessels respond to each heartbeat, in the background, over 30-day periods.
If it finds consistent signs of hypertension, you get a notification to discuss with your healthcare provider. Apple says it cannot identify every instance of hypertension, and it is not intended for people under 22, people already diagnosed with hypertension, or during pregnancy.
Safety1 gain
Fall Detection
GainWhat does this mean?
The watch can sense a hard fall. It taps your wrist, sounds an alarm and shows an alert, so you can call emergency services or tap I'm OK.
If you don't move for about a minute, a 30-second countdown starts; when it ends, the watch calls emergency services and messages your emergency contacts with your location. Apple says it cannot detect all falls. It turns on automatically if you entered an age of 55 or older.
Matters most if: You are 55 or older, or you often work out alone.
Crash Detection
No (same on both)
What does this mean?
The watch can detect a severe car crash, such as a front, side or rear-end collision or a rollover.
After a crash it sounds an alarm and shows an alert. If you don't respond, it calls emergency services and messages your emergency contacts with your location. It needs a cellular connection on the watch or a nearby iPhone, or Wi-Fi calling. Apple says it cannot detect all car crashes.
Matters most if: You drive often, especially alone.
Emergency SOS via satellite
No (same on both)
What does this mean?
On Apple Watch Ultra 3 and later, the watch itself can connect to a satellite when there is no cellular or Wi-Fi coverage, to text emergency services and share your location.
You need a clear view of the sky, and a message can take a few minutes to send. Apple says satellite features are free for 2 years after you activate the watch, and are not offered on models sold in certain countries or regions.
Matters most if: You hike, ski, camp or travel where there is no cell signal.
Design & durability3 changes
Weight by version: Apple Watch Series 3
- 38 mm, aluminum (GPS): 26.7 g
- 38 mm, aluminum (GPS + Cellular): 28.7 g
- 38 mm, stainless steel: 42.4 g
- 38 mm, ceramic: 40.1 g
- 42 mm, aluminum (GPS): 32.3 g
- 42 mm, aluminum (GPS + Cellular): 34.9 g
- 42 mm, stainless steel: 52.8 g
- 42 mm, ceramic: 46.4 g
Weight by version: Apple Watch Series 4
- 40 mm, aluminum: 30.1 g
- 40 mm, stainless steel: 39.8 g
- 44 mm, aluminum: 36.7 g
- 44 mm, stainless steel: 47.9 g
Case sizes
38 mm, 42 mm›40 mm, 44 mm
What does this mean?
The case size in millimeters (mm), measured from the top to the bottom of the case; 10 mm is about 0.4 inch. Most models come in two sizes; Ultra models come in one, 49 mm.
The larger size has a larger screen and weighs a little more. Bands come in sizes too: before you buy one, check that it fits your case size.
Matters most if: You want the largest screen for reading, or the lightest watch to wear all day and night.
Case materials
Aluminum, stainless steel, ceramic (Edition)›Aluminum, stainless steel
What does this mean?
What the case is made of: aluminum, stainless steel, titanium or ceramic depending on the model, or 18-karat gold on the first Apple Watch Edition.
Aluminum is the lightest. Where Apple lists the front glass, aluminum cases have Ion-X glass (Ceramic Shield 2 on Series 12), and stainless steel, titanium, ceramic and gold cases have sapphire crystal. The colors you can choose also depend on the material.
Matters most if: You want the lightest case, or a sapphire front.
Weight (case)
26.7–52.8 g›30.1–47.9 g
What does this mean?
How much the watch case weighs, in grams (g); 28 grams is about 1 ounce. Apple lists a weight for each case size and material, and on some models for the GPS and GPS + Cellular versions.
Comparisons show the lightest to the heaviest case Apple lists; the spec page lists each one. Bigger cases and heavier materials weigh more.
Matters most if: You plan to wear the watch all day and to bed for sleep tracking.
Water resistance
50 m (same on both)
What does this mean?
Apple's water rating. Series 2 and later are rated 50 m (meters) under the ISO 22810:2010 standard; Ultra models are rated 100 m and also meet EN13319, a standard for dive accessories. The first Apple Watch and Series 1 are rated IPX7: splash and water resistant, but Apple does not recommend submerging them.
The rating is not how deep you can go. With a 50 m rating, Apple says you can swim in a pool or the ocean, but not dive, water-ski or go into high-speed water. Apple rates Ultra models for recreational scuba diving to 40 meters (130 feet). Water resistance can wear down over time and cannot be rechecked or resealed.
Matters most if: You swim, snorkel, surf or dive.
IP6X dust resistance
No (same on both)
What does this mean?
IP6X is a dust-resistance rating under the IEC 60529 standard. Apple Watch Series 7 and later and every Ultra model are rated IP6X.
Apple says the rating makes the watch more durable in places like the beach or the desert. It covers dust only; water resistance is rated separately.
Matters most if: You spend time at the beach, in the desert or on dusty trails.
Dive depth
None (same on both)
What does this mean?
The deepest Apple rates the watch for scuba diving. Apple Watch Ultra models are rated for recreational scuba diving to 40 meters (130 feet).
Apple says the Depth app is not a dive computer, that Ultra models should only be used by trained divers, and to use a secondary depth gauge and timer. Series 10 and later show depth only to 6 meters (20 feet), for snorkeling, and Apple says they should not be used for scuba diving.
Matters most if: You scuba dive or free-dive.
What's new
RSS feedAdded Apple Watch and AirPods
Apple Watch and AirPods models checked against Apple's tech specs pages, with comparisons that show only what changes, a page for each model, and their model numbers in Find my model. Apple Watch pages say which iPhone each watch works with; AirPods pages say what the hearing and translation features need. Older models appear on the timeline.
Added information for owners and used buyers
Spec pages now show each model's last security update from Apple's list, any current Apple service program, and for iPhone, the SIM type by country, hearing aid compatibility and Apple's battery lifespan figure. A new page lists ten checks from Apple's support pages before you buy a used iPhone or iPad. The site never asks for a serial number or IMEI.
Added Mac mini, iMac, Mac Studio and Mac Pro
33 desktop Macs from 2017 onward, checked against Apple's tech specs pages, in one Mac section with the laptops, so you can compare a Mac mini with a MacBook Air. Specs a model does not have, such as a screen on Mac mini, show as Not applicable.