What the Shenandoah Trail Difficulty Rating Means
Trail descriptions often label a route "easy", "moderate" or "hard", but those words mean different things to different writers. A numerical rating gives you something more consistent to compare. The Trail Difficulty Rating calculator uses a formula popularised by Shenandoah National Park in Virginia, which folds a trail's distance and climb into a single number, and adds a second figure, Petzoldt's "energy miles". This guide explains both, rates five hypothetical trails, and sets out what the number does not know.
The formula
The Shenandoah rating is:
rating = √(2 × elevation gain in feet × distance in miles)
The calculator takes kilometres and metres, converts them to miles and feet, and applies the formula. The result falls into one of five bands:
- Under 50: easiest
- 50 to under 100: moderate
- 100 to under 150: moderately strenuous
- 150 to under 200: strenuous
- 200 and over: very strenuous
Because distance and gain are multiplied, a trail can be hard by being long, by being steep, or both. Because the result is a square root, doubling both distance and gain doubles the rating, while doubling only one of them raises it by about 41%.
The calculator classifies the rating as it is shown, rounded to one decimal place. A raw value of 49.96 displays as 50.0 and is labelled moderate, so the label never reads easier than the number beside it.
Five trails rated
All distances are for the whole hike (out and back, or the full loop), and gain is the total climbed.
| Trail | Miles | Feet of gain | Rating | Band | Energy miles |
|---|---|---|---|---|---|
| 3 km, 100 m of climb | 1.86 | 328 | 35.0 | Easiest | 2.2 |
| 8 km, 300 m | 4.97 | 984 | 98.9 | Moderate | 6.0 |
| 12 km, 600 m | 7.46 | 1,969 | 171.3 | Strenuous | 9.4 |
| 16 km, 1,000 m | 9.94 | 3,281 | 255.4 | Very strenuous | 13.2 |
| 20 km, 1,500 m | 12.43 | 4,921 | 349.7 | Very strenuous | 17.3 |
A few things to notice:
- The bands fill quickly. An ordinary half-day hike of 8 km with 300 m of climb is already at 98.9, a hair under "moderately strenuous". A full day of 12 km with 600 m is "strenuous". Shenandoah's bands were drawn with that park's trails in mind, and many popular mountain day hikes elsewhere land in the top two bands.
- The top band is open-ended. "Very strenuous" covers both the 255.4 trail and the 349.7 trail, which are very different days. For big routes, compare the numbers, not the labels.
- Small changes add up. The 8 km and 12 km trails are only 4 km and 300 m apart, but the second rates almost 75% higher. Small additions of distance and climb add up fast.
Energy miles
The second figure comes from Paul Petzoldt, the mountaineer and outdoor educator, as a rule of thumb for effort: distance in miles plus one mile for every 1,000 feet of climb. The 12 km trail with 600 m of climb is 7.46 miles plus about 2 for the climb, so 9.4 energy miles. It reads as "this trail feels like walking 9.4 flat miles".
Energy miles are easy to compare with your own experience. If you know you are comfortable walking 10 miles on the flat, a trail with 9.4 energy miles is in range; one with 17.3 probably is not, yet. Our guide to Petzoldt's energy miles looks at the rule in more depth.
Getting the inputs right
The rating is only as good as the two numbers you give it, and both are easy to get wrong.
- Distance is the whole hike. Trail descriptions often give the one-way distance to a summit or lake. For an out-and-back, double it. Entering the one-way figure understates the rating by about 29%, because only one input is halved and the result is a square root.
- Gain is total climb, not summit height. Add up every climb on the route, including climbs on the way back out of any dips. Mapping apps and route-planning sites usually report total ascent; the difference between the trailhead and summit heights is only a minimum.
- Be consistent. Different apps measure gain differently, and some count every small bump while others smooth them out. When comparing routes, take both figures from the same source.
If a trail description already quotes a Shenandoah-style number, check what distance it used. Park-published ratings are worked out for the route as the park describes it, which may be a loop, one way with a shuttle, or out and back.
What the rating cannot see
The formula uses two numbers. Everything else about a trail is invisible to it:
- Footing. A smooth graded path and a boulder field with the same distance and climb get the same rating.
- Steepness profile. 600 m of climb spread evenly over 6 km rates the same as 600 m packed into one steep kilometre.
- Exposure. Drops, narrow ledges and scrambling are not in the number.
- Altitude. The same route at 3,500 m is far harder than at 500 m.
- Heat, snow, ice, mud, river crossings and storms. Conditions on the day can turn a moderate trail into a serious one.
- You. The same number feels different to a fit, experienced hiker and to someone on their first hill walk in years.
Treat the rating as a first filter for comparing routes, not a verdict on whether a route is safe for you today. Read the trail description for footing and exposure, and check the land manager's current conditions, closures and any warnings before you go. If the rangers or the official trail page describe hazards, those override any number.
Using the rating with the other calculators
The rating tells you how hard; it does not tell you how long. For that, use the Hiking Time Calculator. The 12 km trail with 600 m of climb comes out at 3h 24m of moving time by Naismith's rule at average pace, before breaks. Put that into the Daylight Turnaround Calculator for a turnaround time, and into the Water Needs Calculator for a water estimate.
To compare two candidate routes properly, see comparing two hikes by rating, energy miles and time. And if you are working up to harder trails, stepping up to a strenuous hike uses the rating to plan a sensible progression.
A sensible way to read the bands
As a rough guide for adults in reasonable health on good trails in good conditions:
- Easiest suits most people, including beginners and many families.
- Moderate suits people who walk regularly.
- Moderately strenuous and strenuous suit regular hikers with some hill experience.
- Very strenuous is for experienced, fit hikers, and the higher the number, the more experience and preparation it needs.
Whatever the band, carry the essentials, tell someone your route and your expected return time, know the local emergency number, and set a turnaround time. A trail rated "easiest" on a clear day can still be a problem in a storm or after dark.