There is no global standard for trail difficulty in the United States. AllTrails uses crowdsourced star ratings collapsed into easy/moderate/hard. OpenStreetMap uses the SAC hiking scale. The National Park Service uses its own three-tier system. State park systems each invented something different. The result: a trail marked "easy" on one site can be honestly described as "moderate to hard" on another, and a hiker following the optimistic label is going to have a bad day.
This article isn't going to fix the standards problem — that's beyond any single trail directory. What it can do is walk through what each major rating system is actually measuring, where each one fails, and how to read ratings critically before you commit to a hike.
What "difficulty" actually means
Difficulty is a collapsed measure of several distinct underlying factors. The most useful breakdown includes total distance, total elevation gain, terrain technicality (loose rock, exposure, scrambling), trail visibility (will you lose the route?), and the length of any single steep or technical section. Almost every label collapses these five variables into a single word, which is useful as a shortcut and dangerous as a sole filter.
An "easy" 8-mile flat trail and an "easy" 1-mile rocky climb are objectively different experiences with different fitness, gear, and time requirements. Both might earn the same label depending on the rating system.
How AllTrails rates trails
AllTrails uses three tiers — Easy, Moderate, Hard — assigned by a combination of crowd-sourced user reviews and an internal algorithm weighting distance, elevation gain, and user-reported difficulty. The result is generally calibrated to the median user of that platform.
The problem with crowdsourced labels is selection bias. A remote alpine trail in the Sierras might attract only fit thru-hikers, who rate it "moderate" because to them it is. A casual user following that label is going to be wildly out of their depth. Conversely, a popular front-country trail gets reviewed by everyone, including beginners, and skews "hard" because beginners experience steep ground as hard.
Recent AllTrails ratings have gotten more conservative as the platform's user base has broadened, but this calibration drift across years means ratings from 2015 and 2023 mean different things even on the same trail.
How OpenStreetMap rates trails
OSM uses the SAC hiking scale (T1-T6), assigned by volunteer mappers based on observation rather than user surveys. It's more granular than the easy/moderate/hard system and more consistent across regions — a T2 in California should mean the same thing as a T2 in New Hampshire.
The downside: tagging coverage is incomplete. Many US trails simply don't have a SAC scale tag, especially in less-mapped regions. OSM trails default to "no rating" rather than guessing, which is honest but means you can't always rely on the rating field being populated.
How the National Park Service rates trails
NPS uses three tiers per park, calibrated to the park's specific terrain. The complicated part: "moderate" at Acadia means something different than "moderate" at Glacier or Grand Canyon. The labels are internal to each park, not standardized across the system.
Park websites are still the most authoritative source for current conditions and ranger-vetted difficulty. The NPS rating is a good cross-check against third-party platforms — if NPS says "strenuous" and AllTrails says "moderate," trust NPS.
How OutsideAtlas rates trails
Our 4-tier system (Easy / Moderate / Hard / Expert) is derived algorithmically from OpenStreetMap data. The algorithm weights SAC scale, trail visibility, total distance, and total elevation gain, and applies the same rules everywhere — so consistency across regions is guaranteed even when the underlying tagging is uneven.
Where OSM data is missing, we default conservatively. A trail with no difficulty tag gets weighted by its distance and elevation alone, and if both are unknown the trail is left unrated rather than guessed.
Our algorithm is documented on the methodology page for anyone who wants to see exactly how the buckets are derived.
How to read difficulty ratings critically
Three habits will protect you from the rating-system inconsistency problem.
- Always check distance and elevation gain alongside the label. A 12-mile "moderate" trail with 4,000 ft of climb is a different beast than a 4-mile "moderate" with 500 ft of climb. The label collapses; the numbers don't.
- Look at the SAC scale field when present. It's more granular and more consistent than collapsed labels. A T3 means something specific; a "moderate" doesn't.
- Read recent trip reports. Reddit's r/hiking, regional subreddits, and AllTrails reviews from the last 60 days give you the conditions you'll actually face — fresh deadfall, snow patches, washed-out sections.
When ratings disagree
If two sources disagree on a trail's difficulty, default to the more conservative reading. Plan as if the harder rating is correct. The downside of over-preparing is a slightly heavier pack; the downside of under-preparing is the search-and-rescue radio call.
When in doubt, ask a ranger. Park visitor centers have current intelligence that no app does — they hear from the hikers who came out of that exact trail this morning.
One last thought: ratings are a starting point, not a verdict. The hikers who get hurt are rarely the ones who picked something obviously above their level — they're the ones who trusted a single label and didn't dig deeper. Treat difficulty ratings the way you'd treat a movie review: useful signal, but watch the trailer too.
