Energy Miles Explained: Petzoldt's Rule for Hiking Effort
Alongside the Shenandoah difficulty number, the Trail Difficulty Rating calculator reports a second figure: energy miles. It comes from Paul Petzoldt, the American mountaineer who founded the National Outdoor Leadership School, and it is about as simple as a hiking formula can be: take the distance in miles and add one mile for every 1,000 feet of climb. This guide explains why that is useful, compares it with the rating and with Naismith's rule on five hypothetical routes, and shows how much each method charges for climbing.
The idea behind it
Energy miles convert a hilly route into an equivalent flat walk. A route of 7.46 miles with 1,969 feet of climb is about 9.4 energy miles: it should feel roughly like walking 9.4 miles on level ground. That makes it easy to relate an unfamiliar hill route to something you already know. If you regularly walk 10 flat miles without trouble, a route of 9 or 10 energy miles is within your range on distance and climb, though not necessarily on footing or exposure.
Five routes, similar energy miles
Here are five routes, mostly with energy miles close to 9 to 10, alongside the Shenandoah rating and the Hiking Time Calculator's Naismith estimate at average pace.
| Route | Energy miles | Rating | Band | Naismith time |
|---|---|---|---|---|
| 16 km, no climb | 9.9 | 0 | Easiest | 3h 12m |
| 12 km, 600 m | 9.4 | 171.3 | Strenuous | 3h 24m |
| 10 km, 1,000 m | 9.5 | 201.9 | Very strenuous | 3h 40m |
| 6 km, 1,500 m | 8.6 | 191.6 | Strenuous | 3h 42m |
| 20 km, 300 m | 13.4 | 156.4 | Strenuous | 4h 30m |
The table shows three methods measuring three slightly different things.
- The flat route rates zero. The Shenandoah formula multiplies distance by climb, so a route with no climb scores nothing at all, however long it is. Sixteen flat kilometres is a real walk of over three hours; energy miles and Naismith both say so, and the rating does not. For flat or nearly flat routes, ignore the rating and use energy miles or time.
- The steepest route has the fewest energy miles (8.6) but the longest Naismith time of the first four (3h 42m). Petzoldt's rule charges less for climbing than Naismith's does, so on very steep routes energy miles make the day look smaller than it is.
- The rating prefers balance. The 10 km route with 1,000 m of climb rates higher than the 6 km route with 1,500 m, even though the second has more climb, because the rating multiplies the two inputs under a square root.
How much is a climb worth?
Each method effectively converts climb into flat distance at its own rate. Expressed for every 100 m of climb:
- Naismith's rule (5 km per hour, 600 m of climb per hour) treats 100 m of climb as worth about 0.833 km of flat walking.
- Petzoldt's energy miles (one mile per 1,000 feet) treat 100 m of climb as worth about 0.528 km.
So Naismith charges more than half as much again for climbing as Petzoldt does. Neither is right for everyone. Some hikers are strong climbers and find energy miles a good match; others, especially with heavy packs or on rough ground, find even Naismith generous. The best check is your own record: compare your real moving times on a few hilly routes with both figures and see which fits you.
What energy miles are good for
- Comparing with your flat walking. The most intuitive use. If 8 flat miles leaves you comfortably tired, routes up to about 8 energy miles are a sensible range.
- Planning a progression. Adding two or three energy miles at a time is an easy way to build up. See stepping up to a strenuous hike.
- Multi-day trips. Totalling energy miles per day gives a quick check that each day is roughly balanced, and that no day is far beyond the others.
- Talking to a group. "About ten energy miles" is easier for a mixed group to judge than a rating of 171.3.
A worked multi-day check
Suppose a three-day trip with an overnight pack: day 1 is 18 km with 700 m of climb, day 2 is 14 km with 1,000 m, and day 3 is 10 km with 300 m. Running each through the calculators:
| Day | Energy miles | Rating | Naismith, leisurely / heavy pack |
|---|---|---|---|
| 1: 18 km, 700 m | 13.5 | 226.7, very strenuous | 5h 58m |
| 2: 14 km, 1,000 m | 12.0 | 238.9, very strenuous | 5h 35m |
| 3: 10 km, 300 m | 7.2 | 110.6, moderately strenuous | 3h 08m |
The numbers say the first day is the biggest by energy miles and time, on the day the pack is heaviest with full food. That is a common planning mistake: front-loading the hardest day before your legs have settled and while the food bag is at its heaviest. Moving the camp a few kilometres earlier on day 1, and adding the distance to day 3, would even the trip out. The rating ranks day 2 slightly above day 1 because of its extra climb, which is worth knowing too: day 2 is the steeper day and will feel like it.
What they are not good for
- Timing. Energy miles are not hours. For time, use the Hiking Time Calculator, add breaks, then set a turnaround with the Daylight Turnaround Calculator.
- Very steep routes. As the table shows, they undercount steep climbs compared with Naismith.
- Descents. Petzoldt's rule, like Naismith's, adds nothing for going down. A steep, rough descent can be slow and hard on the knees.
- Anything beyond distance and climb. Footing, exposure, scrambling, altitude, heat, snow and the weather on the day are all outside the formula.
Before any real hike, read the trail description and check the land manager's current conditions, closures and warnings. If they describe hazards that the numbers cannot, such as river crossings, exposed sections or seasonal snow, those decide whether the route suits you.
Using all three together
The three numbers complement each other. Energy miles relate a route to your flat walking. The Shenandoah rating places it in a band for comparing with other trails, as long as it has some climb. Naismith's time tells you how long to plan for. When they agree, you can be confident about the size of the day. When they disagree, as on the flat route and the very steep one above, it is a sign the route is unusual in some way, and worth a closer look at the map. Our guide to comparing two hikes works through a disagreement in detail.
Whichever number you lead with, the day still needs the same basics: water and food planned for the hours, not the miles; the ten essentials; a turnaround time; your route and return time left with someone at home; and the local emergency number in your phone.