Free Pace Calculator for Trail and Ultra Distances¶
Type 50 miles and 13 hours into a free pace calculator and it prints 15:36 per mile. That number is correct and you will not run it. Not once, not for a single mile of the day.
You will run 11:30 on the runnable stuff early. You will hike a climb at 24:00. You will stand at an aid station for six minutes with a cup of broth while the clock keeps counting. Add all of that up and divide by 50 and you get 15:36, which is the arithmetic of your whole day and not an instruction for any part of it.
That gap is why generic pace math has a bad reputation on trail. The math is fine. What it needs is three adjustments before you type anything in, and then you run it once per segment instead of once per race.
The NavRun pace calculator is free and takes no signup, so you can have it open in another tab while you work through this.
What a free pace calculator does, and where it stops¶
Pace is time divided by distance. Give the tool any two of distance, time, and pace and it solves for the third, then lays out a split table showing what your cumulative time should read at each checkpoint. It goes from 5K to 100 miles, and there is a custom-miles box for the distances that are not on anyone's dropdown.
Two things about the split table are worth knowing before you use it on a long day:
- Up to the marathon it gives you one row per mile. Past the marathon it switches to five-mile checkpoints, because a 100-row table is not something you read at mile 62.
- Every row assumes even effort on flat ground. Every row.
That second line is the whole limitation. Flat ground is the assumption underneath the number, and the assumption is what a trail race breaks. Five things break it, in rough order of how much time they move:
| What breaks it | What it does to the number |
|---|---|
| Climbing | Adds time the distance column cannot see |
| Standing still | Aid station minutes are in your finish time and not in your pace |
| Hiking | A deliberate choice that reads on the watch like falling apart |
| Descending | Gives back some time, and much less late in the day |
| Dark | Your usable line of sight shortens and your feet get careful |
None of that makes the calculator wrong. It makes the raw output an average you need to take apart before it is useful. On a road race you can mostly skip that step, and how to use a pace calculator for even splits covers that version.
Adjustment one: turn your vert into flat miles before you type¶
The oldest workable trick here is Scarf's rule, from a 2007 study of hill-running records: 1,000 feet of climbing costs about the same as half a mile of flat running. It is the same rule NavRun uses internally when it adjusts a predicted finish time for a course profile.
So before you enter a distance, convert the course into what it would be on flat ground:
Flat-equivalent miles = course miles + (feet of gain / 1000 × 0.5)
| Race | Miles | Gain | Flat-equivalent |
|---|---|---|---|
| Rolling 50K | 31 | 3,500 ft | 32.8 mi |
| Mountain 50K | 31 | 6,500 ft | 34.3 mi |
| Mountain 50 mile | 50 | 9,000 ft | 54.5 mi |
| Big mountain 100 | 100 | 18,000 ft | 109 mi |
Now enter the flat-equivalent number instead of the course distance. For that mountain 50 miler with a 13-hour goal, 54.5 miles and 13 hours gives you 14:19 per mile. That is the flat-ground effort you would need to be able to hold. The 15:36 the raw distance produced was never a pace you could compare to anything in your training log. 14:19 is, because your training log has flat miles in it.
This works in the other direction too, and that direction is more honest. Pick the mode that solves for finish time, enter the flat-ground pace you know you can hold for a long day, and let it tell you what the course costs you. You are handing it a number you have proved instead of a number you hope for.
Adjustment two: take out the time you are standing still¶
This is the one nobody does, and it is worth more than the vert adjustment on a race with a lot of stops.
Your finish time includes every minute you spend at aid stations. Your pace does not care where the minutes went. Eight aid stations at six minutes each is 48 minutes, and on a 13-hour, 50-mile day that 48 minutes is 58 seconds of every single mile.
Same 50 miler, same 13-hour goal:
| Version of the number | Pace |
|---|---|
| Raw: 50 miles, 13 hours | 15:36/mi |
| Moving only: 50 miles, 12:12 | 14:38/mi |
| Moving and flat-equivalent: 54.5 miles, 12:12 | 13:26/mi |
Two minutes and ten seconds per mile separates the first row from the last. The first row is what a pace calculator prints when you hand it the race distance and your goal. The last row is what you have to be capable of. Both are true and only one of them is checkable against anything you have ever run.
The arithmetic is short enough to do on the back of a drop bag list:
- Count the aid stations on the course map.
- Guess your time at each one, honestly. Most people are slower than they think. Six minutes is a fast, practiced stop. Ten is normal. A crewed stop with a shoe change is fifteen.
- Multiply, and subtract that from your goal time.
- Put the leftover into the calculator as your time, and the flat-equivalent distance as your distance.
If you have never timed an aid station stop, how you handle aid stations is the other half of this. The stop is a real part of the race and it belongs in the budget rather than in the surprise.
Adjustment three: run it once per segment, not once per race¶
One average across 50 miles hides everything that matters. A trail race is a set of segments with different personalities, and aid stations are already the natural boundary, because the cutoff sheet is written in arrival times at aid stations anyway.
So use the calculator once per segment. Take the segment's miles, add its own vert, get a flat-equivalent distance, and give it a slice of the moving budget.
Here is the same mountain 50 miler broken up. Total moving budget 12:12, spread across 54.5 flat-equivalent miles, which is 13:26 per flat-equivalent mile.
| Segment | Miles | Gain | Flat-equiv | Moving budget | Real pace | Clock on arrival |
|---|---|---|---|---|---|---|
| Start to Aid 3 | 0 to 14 | 3,200 ft | 15.6 | 3:29:32 | 14:58/mi | 3:42 |
| Aid 3 to Aid 5 | 14 to 28 | 2,400 ft | 15.2 | 3:24:09 | 14:35/mi | 7:18 |
| Aid 5 to Aid 7 | 28 to 40 | 2,600 ft | 13.3 | 2:58:38 | 14:53/mi | 10:28 |
| Aid 7 to finish | 40 to 50 | 800 ft | 10.4 | 2:19:41 | 13:58/mi | 13:00 |
The clock column includes six minutes at every aid station along the way, which is why it lands on 13:00 and the moving column lands on 12:12. That last column is the one to write on your arm. It is in the same units as the cutoff sheet.
Now look at the last row and be honest about it. On paper the closing 10 miles are your fastest segment, because they have the least climbing. In the race they will be your slowest, because they come after 40 miles. That is the thing the arithmetic cannot know.
The fix is to move the budget by hand. Take 15 minutes out of the first two segments and give it to the last one. You go out slower than the flat math says and you arrive at mile 40 with something in your pocket. Nobody has ever regretted that trade at mile 45.
Descents give back less than you think¶
The tempting move after the vert adjustment is to subtract for the downhills. Be careful with it.
Real-world data on a lot of runners caps the benefit of net descent at around 10 percent of your flat time, and only on a course that drops more than it climbs. NavRun's own elevation math uses that 10 percent ceiling for the same reason: the gain side of a course is close to linear, and the give-back side flattens out fast. A 3,000-foot climb costs you about what it costs. A 3,000-foot descent does not hand it back.
There is a second thing the arithmetic will not tell you. A descent at mile 8 and a descent at mile 42 are the same contour lines and different events. Late in a race, quads that have already absorbed 6,000 feet of downhill will not let you use the grade. Budget the last descent of the day closer to your flat pace than to your fresh descending pace, and if the course has a long drop in the final quarter, prepping the quads for it does more for your finish time than any pacing table will.
Night miles get their own number, and it is yours¶
Everything above is a rule of thumb applied to a course profile. Night is the one where general rules are worth less than what you already have on your watch.
Your headlamp gives you a cone. On technical trail that cone is shorter than your daylight line of sight, so your feet get careful and your pace changes. How much it changes is personal to a degree that no published constant covers. Some runners lose very little. Some lose a lot on rock and almost nothing on smooth singletrack.
Which means the honest source is your own log. If you have run in the dark on similar terrain, pull those runs up, compare them against your daylight runs on the same trails, and use that ratio for the segments that fall after sunset. If you have never run at night on terrain like the course, that is not a gap in your training so much as a gap in your data, and it is one long evening run away from being filled. There is more on the rest of it in running an ultra at night.
Budget the night segments separately either way. Applying your daylight pace to the hours between 10pm and 5am is the most common way a segment plan comes apart.
What the number is for¶
A pace table is not a verdict on you. It is a budget, and a budget exists so you can spend against it on purpose.
The reason to do this arithmetic before race day is that on race day you get one number to check at each aid station: what time is it, and what time did I plan to be here. That is a much smaller question than "am I doing okay", and it is answerable in two seconds by a person who has been awake for 19 hours.
It also works in the direction most people forget. When you are 40 minutes ahead of your budget at mile 28, the table tells you to eat something and stop pressing. When you are 20 minutes behind and the cutoff is two hours away, the table tells you that you are fine, which is a thing worth knowing at the moment your brain has decided you are not.
And a long, slow finish is a long day of work. Thirty hours on your feet is thirty hours on your feet. The per-mile figure attached to it is arithmetic, not a grade. Time on feet is the measure that carries across from your training log to a hundred-mile day, and pace is the number that happens to fall out of it.
Common questions¶
Is the pace calculator free?¶
Yes. No account, no email required to use it. Enter any two of distance, time, and pace and you get the third plus a full split table. There is an option to email the splits to yourself if you want them on your phone on race morning, and you can save the result as an image.
Can a pace calculator handle 50K, 100K, and 100 miles?¶
The NavRun one has 50K, 50 mile, 100K, and 100 mile in the distance list, plus a custom-miles box for anything else. Past the marathon the split table switches to five-mile checkpoints so it stays readable. For a trail race, use the custom box with your flat-equivalent distance rather than the listed one.
How do I convert elevation gain into pace?¶
Use the flat-equivalent conversion: every 1,000 feet of gain adds roughly half a mile of flat-ground distance. Add that to your course distance and use the total. It is a rough rule that holds up well across most trail courses, and it is far closer than ignoring the vert.
Why is my trail pace so much slower than my road pace?¶
Because trail is different ground, not because you got slower. Terrain, gradient, and footing all cost time at the same effort. Trail versus road pace covers the size of the gap. The point of the flat-equivalent conversion is to get your trail number and your road number into the same units so you can compare them at all.
Should I plan even splits for an ultra?¶
Plan even effort, and expect the clock to show a fade. Almost everyone runs the second half of a hundred slower than the first, so an even-split table is a starting shape rather than a target. Move a chunk of time from your early segments into your late ones before you print it.
What if I do not know my goal time yet?¶
Run it backwards. Enter a pace you know you can hold for a long day and let the tool give you the finish time. If you want a goal built from your training instead of a guess, the race time predictor works from a recent race and adjusts for ultra distances.
Does hiking ruin my average pace?¶
Hiking is part of the plan on any course with real climbing, and the average absorbs it. That is what the flat-equivalent conversion is for: the climb shows up as extra distance, so the slow segment pace is expected rather than alarming. Power hiking is a trainable skill and most people are faster at it than they think once they practice.
Take the number apart before you trust it¶
Three adjustments, in order:
- Vert. Add half a mile of flat-equivalent distance for every 1,000 feet of gain, then enter that.
- Stops. Subtract your aid station minutes from the goal time before you divide.
- Segments. Run the calculator once per aid-station leg, and write the arrival clock times on your arm.
Do that and the free pace calculator stops printing a number you will never run and starts printing a plan you can check against a cutoff sheet.
Start with the pace calculator. It costs nothing and wants no account.
Then, if your training is logged in Strava, connect it to NavRun and the same math runs against your real last eight weeks instead of a guess: your own long runs, your own vert per mile, your own time on feet. Building a training plan from it costs nothing either. The calculator tells you what a goal requires. Your training log is the only thing that can tell you what is already yours.