How to Convert Road Pace to Trail Pace: The Real Numbers

How to convert road pace to trail pace: the flat-equivalent rule, Naismith for runners, grade-adjusted pace, and a slowdown table by vertical gain per km.

Converting road pace to trail pace is the calculation every road runner gets wrong on their first trail race. They hold a 4:45 min/km marathon pace, look at a 30 km trail race with 1,200 m of climbing, and plan for two and a half hours. They finish in three hours forty. The mistake is treating elevation as a modest penalty rather than the dominant variable. This guide gives you three methods for converting road pace to trail pace, from a back-of-envelope rule to the physiology-based version, and tells you which to use when.

Why the conversion is hard

The energy cost of running changes non-linearly with gradient. At a 45% incline it costs roughly 5.6 times what level running costs per metre travelled, while at a 20% descent it costs about half (Minetti et al., 2002).

Two consequences follow.

Climbing does not slow you proportionally, it slows you steeply. Doubling the gradient does considerably more than double the effort.

Descents do not give the time back. Even on the most economical gradient, terrain, braking, and quadriceps fatigue prevent you converting the metabolic saving into speed. A course with equal ascent and descent is always slower than its flat equivalent.

Method one: converting road pace to trail with the flat-equivalent rule

The quickest method, and accurate enough for planning.

Add 100 metres of flat-equivalent distance for every 10 metres of vertical gain.

Put another way, treat every 100 m of climbing as an extra kilometre of flat running.

Worked example. A 30 km trail race with 1,200 m of climbing.

  • Flat-equivalent distance: 30 + 12 = 42 km
  • At a road pace of 5:00 min/km for that distance, that is 3 hours 30 minutes

Compare with the naive calculation of 30 km at 5:00, which gives 2:30. The difference is an hour, and it is the difference between a good day and a disaster.

This is close to the ITRA concept of kilometre-effort, which adds elevation gain divided by 100 to the distance (International Trail Running Association, 2026). Race organisers use it precisely because it produces sensible comparisons between courses.

Adjust the ratio for terrain:

  • Smooth, runnable trail: 100 m of vert per kilometre added
  • Mixed trail with some technical sections: 100 m vert per 1.2 km added
  • Steep, technical mountain terrain: 100 m vert per 1.5 km added

Method two: Naismith's rule, adapted

Naismith's rule comes from Scottish hillwalking and still works well for long, slow efforts.

Allow one hour per 5 km of distance, plus one hour per 600 m of ascent.

Runners need to scale the base rate to their own speed, keeping the vertical component roughly intact.

Adapted for runners:

Time = (distance in km / your flat trail speed in km/h) + (vertical gain in m / your climbing rate in m/hr)

Typical climbing rates, or vertical ascent metres per hour:

  • Recreational trail runner on a sustained climb: 400 to 600 m/hr
  • Well-trained trail runner: 600 to 900 m/hr
  • Elite mountain runner: 1,000 to 1,500 m/hr

Worked example. A trained runner covering 25 km with 1,500 m of climbing, moving at 9 km/h on the flat and 700 m/hr climbing.

  • Horizontal: 25 / 9 = 2.78 hours
  • Vertical: 1,500 / 700 = 2.14 hours
  • Total: roughly 4 hours 55 minutes

This method is better than the flat-equivalent rule for very steep courses, because it separates the two variables rather than blending them.

Our vertical pace guide covers how to measure your own climbing rate.

Method three: gradient-adjusted pace

Platforms that report grade-adjusted pace apply a version of the Minetti energy cost curve to your GPS track, converting each segment into the flat pace that would have cost the same energy.

What it is good for:

  • Comparing efforts across different routes
  • Checking whether an easy run stayed easy despite hills
  • Tracking fitness on varied terrain

What it is not good for:

  • Predicting race times, since it ignores fatigue accumulation, technical footing, and the fact that you cannot sustain flat-equivalent effort for eight hours
  • Descents, where it credits you with speed you cannot mechanically produce on rough ground

Treat grade-adjusted pace as a training analysis tool, not a race planner.

What none of the methods capture

Technical footing. Rocks and roots slow you independently of gradient, and the effect grows with fatigue (Vernillo et al., 2017).

Fatigue accumulation. All three methods assume steady output. Over six hours, output falls, and the drop is larger on courses with heavy descent.

Altitude. Above 2,000 m, sustainable pace drops noticeably.

Heat. Above 25 C, expect a 5 to 15% slowdown.

Aid station time. Ten stops at four minutes is 40 minutes of wall clock time no formula accounts for.

Night running. Speed on technical ground drops 10 to 20% in darkness.

This is why formulas underestimate ultra times consistently. Trailia's Race Predictor builds these factors in alongside your actual training data, which is why its estimates tend to be slower and more accurate than a spreadsheet.

A conversion table to start from

Approximate slowdown against your flat road pace, for a moderately technical trail:

Vertical gain per km Slowdown vs road pace
0 to 10 m/km 5 to 10%
10 to 20 m/km 15 to 25%
20 to 30 m/km 25 to 40%
30 to 50 m/km 40 to 70%
Over 50 m/km 70 to 120%

A 42 km race with 2,700 m of climbing sits at 64 m/km, which is why Zegama finishers take roughly double their road marathon time.

Key takeaways

  • Treat every 100 m of vertical gain as an extra kilometre of flat running
  • For steep courses, use Naismith's method, separating horizontal speed from climbing rate in m/hr
  • Grade-adjusted pace is a training analysis tool, not a race predictor
  • Descents never give back the time the climbs cost
  • Add allowances for technical ground, heat, altitude, darkness, and aid station stops

Where to go from here

Calculate your own climbing rate on a sustained hill this week: time a climb, divide the vertical gain by the hours, and you have a personal m/hr figure that makes every future estimate considerably more accurate than a generic multiplier.

For race planning specifically, Trailia converts your recent training into a course-specific prediction rather than a formula, accounting for the fatigue and terrain that the arithmetic above deliberately ignores.

Citations

  • Minetti, A. E., Moia, C., Roi, G. S., Susta, D., & Ferretti, G. (2002). Energy cost of walking and running at extreme uphill and downhill slopes. Journal of Applied Physiology, 93(3), 1039-1046.
  • Vernillo, G., Giandolini, M., Edwards, W. B., et al. (2017). Biomechanics and Physiology of Uphill and Downhill Running. Sports Medicine, 47(4), 615-629.
  • Scheer, V., Basset, P., Giovanelli, N., Vernillo, G., Millet, G. P., & Costa, R. J. S. (2020). Defining Off-road Running: A Position Statement from the Ultra Sports Science Foundation. International Journal of Sports Medicine, 41(5), 275-284.
  • International Trail Running Association (2026). Kilometre-effort and race categorisation documentation.

Frequently Asked Questions

How much slower is trail running than road running?

It depends almost entirely on vertical gain per kilometre. At 10 to 20 metres of climbing per kilometre expect 15 to 25% slower than road pace, while above 50 m/km you are looking at 70 to 120% slower. A race with 64 metres of gain per kilometre, like Zegama, takes roughly double a road marathon time.

What is the easiest way to convert road pace to trail pace?

Treat every 100 metres of vertical gain as an extra kilometre of flat running. A 30 km race with 1,200 metres of climbing becomes a 42 km flat-equivalent, so at 5:00 min/km that is 3 hours 30 rather than the 2:30 the raw distance suggests. Adjust upward for technical terrain.

What is Naismith's rule for runners?

The original hillwalking rule allows one hour per 5 km plus one hour per 600 metres of ascent. Adapted for runners, divide distance by your flat trail speed in km/h and add vertical gain divided by your climbing rate in metres per hour. It works better than flat-equivalent rules on very steep courses.

What is a good climbing rate in metres per hour?

Recreational trail runners typically sustain 400 to 600 metres per hour on a long climb, well-trained runners 600 to 900, and elite mountain runners 1,000 to 1,500. Measuring your own rate on a sustained hill makes every future race estimate considerably more accurate than using a generic multiplier.

Do descents make up for the time lost climbing?

No. Even at the most economical downhill gradient, technical footing, braking demands, and quadriceps fatigue prevent you converting the metabolic saving into speed. A course with equal ascent and descent is always slower than its flat equivalent.

Is grade-adjusted pace accurate?

It is useful for comparing efforts across routes and checking that easy runs stayed easy, since it applies an energy cost curve to your GPS track. It is poor for predicting race times, because it ignores fatigue accumulation, technical footing, and the fact that you cannot hold flat-equivalent effort for eight hours. Treat it as an analysis tool rather than a planner.

Why do pace formulas underestimate ultra finish times?

They assume steady output, which nobody sustains over six or more hours. They also ignore technical footing, altitude above 2,000 metres, heat above 25 C, night running which cuts speed by 10 to 20% on technical ground, and aid station time. Ten stops at four minutes each is 40 minutes no formula accounts for.

What is kilometre-effort?

A metric used by ITRA and many race organisers that adds elevation gain divided by 100 to the distance in kilometres. A 30 km race with 1,200 metres of climbing scores 42 kilometre-effort. It exists precisely so that courses with very different profiles can be compared sensibly.

How much does heat affect trail pace?

Above 25 C, expect a 5 to 15% slowdown, with the effect growing as temperature and humidity rise. Heat acclimation reduces but does not eliminate the penalty. Build it into your estimate rather than discovering it in the second half of the race.

Should I plan my race by pace or by effort?

By effort, always, on terrain with significant elevation change. Pace targets on climbs push you into unsustainable intensity early and pace targets on descents encourage reckless quadriceps damage. Use converted pace for planning your total time and use effort to execute on the day.