The best GPS watches for ultra running

Why this page is not the trail page

Our trail ranking is about positioning and navigation: whether the watch holds a track under tree cover and whether it can show you a map when you are lost. This page is about one thing only, which is duration. A 100-mile race is 20 to 36 hours of continuous recording for most finishers, and that is longer than the honest specification on several watches marketed for exactly this purpose.

So the useful thing we can do is the thing makers avoid doing: put every published figure next to the satellite mode it actually describes.

Every stated figure, with the mode named

Read the third column before the second. The Polar number is the largest on the page and it is also the least specific: Polar publishes 43 hours of training with GPS without telling us whether that is single-band or dual-frequency, and those two modes differ by roughly a factor of two on watches that do publish both. We carry the figure because it is what Polar states, and we say what it does not tell you.

The COROS pair make the opposite point. The PACE Pro is the only watch in the COROS line with a published dual-frequency endurance figure, at 31 hours — and the cheaper, newer PACE 4 publishes 41 hours in All-Systems mode and nothing at all for dual-frequency. The bigger headline number belongs to the watch with the less informative specification.

Solar is the only thing here that changes the arithmetic

Garmin publishes five different GPS figures for the Instinct 3 Solar, and the difference between the flattering one and the honest one is enormous: 130 hours GPS-only with solar assistance against 24 hours in all-satellite multi-band without it. We carry 24 everywhere on this site, deliberately, because the solar figures assume sustained bright light and the multi-band mode is the one you bought a modern receiver for.

For an ultra that distinction has a specific shape. Solar assistance helps exactly when the course is open and sunlit, and stops helping at dusk — which is when you switch the backlight on, start navigating, and need the watch most. Treat the solar figure as a bonus you may get and the 24-hour figure as the number you plan with.

The always-on display tax

The other published figure worth planning around is the screen. Garmin's own table takes the fēnix 8 from 35 stated multi-band hours with the Gesture timeout to 28 with the display always on. COROS states that the PACE Pro goes from 20 days of daily use to 6 full days with its always-on display enabled.

That is a real choice, not a rounding error. Twenty percent of your recording time is the price of not flicking your wrist, and in the back half of a long race, flicking your wrist is not free either. Our PACE Pro review works through the COROS version of this trade in detail.

Cost per hour of recording

This is the arithmetic that makes an endurance ranking checkable rather than asserted: the live price divided by the maker's own stated hours, in the mode named above. The Instinct 3 Solar comes to $12.50, the PACE 4 to $6.07, the fēnix 8 to $21.40, the Grit X2 Pro to $16.28 and the PACE Pro to $9.65.

Those are not like-for-like, because the modes are not like-for-like, and we would rather show you the working than hand you a single ranked column that quietly compares a dual-frequency figure against an unnamed one. The gap between the cheapest and the most expensive watch on this page is $500 today.

What none of these watches fix

Heart rate over 24 hours. Wrist optical accuracy is the weakest link in the whole chain, and a swollen, cold, wet arm at hour 20 is the worst case for it. Nothing on this page has an independent wrist-heart-rate validation we could find. If the heart rate matters to your pacing, a chest strap costs a fraction of any of these watches.

The estimates. Training load, VO2 max and threshold numbers derived over a multi-day event are extrapolations of algorithms that were never validated on anything like it. We cover what has and has not been measured in VO2 max accuracy by device.

Charging on the move.Every watch here can be charged from a battery pack mid-race, and every one of them has a proprietary cable. The cable, not the watch, is the thing that actually ends people's data at mile 70.

Choosing between the five

If your races are under about 24 hours and you want the cheapest honest answer, the PACE 4 publishes 41 All-Systems hours for the lowest price here. If you want maps and dive-rated ruggedness with the longest well-specified multi-band figure, the fēnix 8. If your events are multi-day and largely in daylight, the Instinct 3 Solar is the only watch whose maker publishes an expedition mode measured in days. The Grit X2 Pro is the highest raw number and the least specific one, and the PACE Pro is the only COROS that tells you what dual-frequency actually costs.

How to plan an ultra watch purchase

• Start from your slowest realistic finish time, not the course record. Then add the pre-race standing around and any navigation you will do on the watch.
• Use the mode you will actually record in. If you bought a multi-band receiver and then run in GPS-only to save battery, you paid for a specification you are not using.
• Do not plan with a solar figure. It is a real number under bright light and it is not a number you can count on at 3 a.m.
• Carry the cable. Every watch here charges from a pack while worn, and the cable is proprietary to the brand.

Every score here comes from the same rubric applied to every device on the site — evidence, hardware, metric coverage, endurance and cost per capability, with the weights published at how we rank. We have not run an ultra in any of these watches and we never claim to have.