A 100-mile race lasts 18–30 hours. A 200-mile race lasts 60–100. The watch you wear has to outlast the race, accurately, with GPS on and HR sampling. That eliminates 80% of the GPS watches on the market. Below, the five we'd actually wear at mile eighty, sorted by overall pick.
The picks
Garmin
Garmin Fenix 8 (Solar / 51mm)
The watch most ultra finishers actually wear. Three-day battery in GPS-on, real solar charging, the most accurate elevation tracking we've measured.
- Up to 48 hours of GPS battery (Solar, all-systems)
- Built-in topo maps + offline routing
- Pulse-ox sleep tracking + multi-band GPS
- AMOLED screen — readable in noon sun
COROS
COROS Apex 2 Pro
The COROS faithful are right. 75-hour all-systems GPS battery, lightweight (66g), and the simplest UI in the category. Half the price of a Fenix 8 with most of the function.
- 75 hr all-systems GPS battery
- Sapphire glass face
- Touchscreen + dial control
- Strava + TrainingPeaks sync
Suunto
Suunto Vertical (Titanium Solar)
The longest battery life on the market for an ultra-distance race. 60-day standard mode, 90 hours of GPS. Topo maps free for life. Built for UTMB / Hardrock conditions.
- 90 hr all-systems GPS (Solar)
- Free worldwide topo maps
- Titanium bezel — bombproof
- Best-in-class barometric altimeter
Apple
Apple Watch Ultra 2
The only ultra watch that doubles as a real iPhone-tier device. 36-hour battery is enough for most 100-milers; 72 hours in low-power mode covers Western States. Best UX, smallest learning curve.
- 36 hr battery (low-power 72 hr) — fits most 100s
- Live cellular + Apple Pay on-trail
- Best-in-class call quality + integration
- Workout API support for every major training app
Polar
Polar Vantage V3
Polar still has the best wrist-based HRM in the category. If you train by heart-rate first and pace second, Vantage V3 is the right call. AMOLED screen + dual-band GPS, training-load science nobody else has.
- 61 hr GPS battery
- Best-in-class wrist HRM (4th-gen optical)
- Polar Flow training-load + recovery science
- AMOLED touchscreen
Battery is the only spec that matters
Marketing departments push "1080 lumen displays" and "octa-core processors." For ultras, none of this matters. The only spec that matters is GPS-on battery life with HR sampling enabled, the way you'll actually use it. Real-world numbers (subtract ~20% from manufacturer claims):
- Garmin Fenix 8 Solar: ~38 hours real-world
- COROS Apex 2 Pro: ~58 hours real-world
- Suunto Vertical Solar: ~70+ hours real-world
- Apple Watch Ultra 2: ~28 hours real-world (low-power: ~58)
- Polar Vantage V3: ~50 hours real-world
For a 24-hour goal at Western States, any of the above. For a Hardrock 38-hour finish, drop the Apple Watch unless you'll switch to low-power. For Cocodona's 90-hour effort, only Suunto Vertical or COROS will survive without a charging stop.
Multi-band GPS is non-negotiable for mountain ultras
Single-frequency GPS produces wildly inaccurate elevation readings under tree cover and on ridge-walks. Multi-band (L1 + L5) corrects for atmospheric distortion and cuts the noise. All five watches above support multi-band. If you're considering a watch that doesn't, walk away.
Wrist HRM vs chest strap
Wrist HRM is fine for easy training and Zone 2 work. For race-day HR data — the data you'll actually use to make pacing decisions — chest strap is more accurate. The Polar H10 ($90) pairs with all five watches above and adds maybe 10g of weight to your kit.
Should I buy a $1,100 watch?
Honest answer: only if you're racing 100s+ regularly. The Fenix 8 is the best ultra watch on the market, but the COROS Apex 2 Pro at $499 covers ~95% of what most ultrarunners need at less than half the price. The premium Garmin gets you sapphire glass, deeper map integration, and a flashlight (genuinely useful at night). Worth it if you're running 4+ ultras a year. Hard to justify for one race.
What we don't recommend (and why)
Garmin Forerunner 970: a great running watch, but optimized for marathon-distance — battery drops fast in 100-mile races. Get the Fenix instead.
Garmin Instinct 3: entry-level battery is too short for ultras. The look is great but the spec doesn't keep up.
Whoop strap: excellent recovery tool, no GPS. Wear it as a complement to a real watch, not as a replacement.