The Forerunner 255 is the first watch in Garmin's mid-tier running line that actually deserves to be called a triathlon watch. Its predecessor, the 245, was a running watch with a swim mode bolted on. The 255 adds real multisport support — swim, bike, run, and full triathlon profiles — without pushing you into Garmin's much pricier Forerunner 955 or Fenix territory.
If you're training for your first 70.3 or full-distance race and don't need built-in maps or the full Garmin flagship feature set, this is very likely the watch worth buying.
Key specs
| Case sizes | 41mm (255S) or 46mm (255) |
| Weight | 39g (255S) / 49g (255) |
| Display | Memory-in-pixel (always-on, lower power than AMOLED) |
| Water rating | 5ATM |
| Battery life | Up to 12–14 days smartwatch mode, 26–30 hours GPS-only |
| GPS | Multi-band GPS (same as Garmin's Fenix 7/Epix 2) |
| Price | Around £300 (base model), music editions cost more, but can be less on sites like Backmarket |
What it does well
Multisport, properly. Pool and open-water swim tracking (stroke count, SWOLF, distance), full cycling metrics with power meter compatibility, and dedicated triathlon mode that transitions between disciplines. It's genuinely built for race day, not just training.
Battery life that respects long training blocks. 26–30 hours in GPS mode comfortably covers a full Ironman with room to spare, and multi-day smartwatch battery means you're not charging it every night during a heavy training week.
The small size option. The 255S, at 39g, is one of the lightest full-featured GPS watches Garmin makes — a genuine option for anyone who's found bigger multisport watches uncomfortable on smaller wrists.
Smarter race-day guidance. Set a race date and the 255 adjusts its training load recommendations and recovery guidance around it, rather than just tracking generic fitness trends.
Where it falls short
- No touchscreen — everything is button-based, which some find slower for navigating menus (though it does mean no accidental swipes mid-swim)
- No built-in maps or turn-by-turn navigation, unlike the pricier Forerunner 955 or Fenix line
- No solar charging option
- Heart-rate accuracy while swimming, like most wrist-based sensors, isn't fully reliable — a chest strap is still the better option if you need precise HR data on the bike or run
Who it's for
Anyone doing their first triathlon or 70.3 who wants genuine multisport tracking without paying for features (offline maps, advanced cycling dynamics) they won't use yet. If you're already racing full-distance events competitively and want L/R power balance or onboard maps, look at the Forerunner 955 instead.
The verdict
Having purchased a refurbished one through BackMarket, I am amazed by the performance of the watch for the £170 I paid. The battery lasting 14 days is a great benefit and the ease of use means it works for those new to triathlon training and experienced, and the data recorded in the app allows you to narrow down all aspects of your training.
Best for: first-time triathletes, budget-conscious multisporters