Dead-reckoning is the simplest navigation skill. It’s much easier to learn than reading a map, or operating a compass, GPS, or altimeter watch.
Yet I find it to be one of the most useful and frequently used, especially when hiking on well-maintained trails where a consistent physical effort yields consistent results. Such trails include well-known long-distance footpaths (e.g. Appalachian, John Muir, Wonderland) and most trails in National Parks and high-use Wilderness Areas (e.g. Yellowstone, Indian Peaks).
This technique is less useful when hiking off-trail or on trails with extreme vertical change. Off-trail terrain is more variable (i.e. it’s sometimes great, sometimes awful), so results are less predictable. And in extremely mountains environments, forward progress is more a function of vertical hiking speed (e.g. 30 vertical feet per minute), and the horizontal distance over which this vertical change happens is less relevant (if not entirely irrelevant).
I use dead-reckoning to:
- Predict ETA at future landmarks, like water sources, trail junctions and campsites;
- Approximate my current location relative to the last or next landmark; and,
- Rule out “false” features like false summits and unmarked trail junctions.
In general, regular dead-reckoning helps to to “stay found” because it sets expectations about what should be happening. If reality does not match expectations (e.g. did not reach a landmark when expected, or reached a different landmark than expected), it’s a cause for a map-check.
To dead-reckon, two out of three following items are needed:
- Distance between two landmarks, derived from a topographic map, databook, or guidebook;
- Rate of travel, which can be measured (e.g. with a GPS unit) or calculated on past trips; or,
- Time, using a simple watch (although if you want to get serious about backpacking, I recommend a GPS sports watch).
Advanced tip: In mountainous environments, it is useful to know the vertical change between two landmarks, because this factor may influence your calculations. Vertical change between two points can be quickly measured on a map so long as the gradient is consistently up or down; in rolling terrain, vertical change calculations are more time-consuming.
How to dead-reckon
You might recall this formula from high school physics: Distance = Rate * Time, whereby:
- Distance = miles or kilometers
- Rate = MPH or KPH
- Time = Hours
The main formula can be reconfigured to solve for other variables:
- Rate = Distance / Time
- Time = Distance / Rate
To dead-reckon, essentially you insert two known variables to determine the third.
Tip: It’s useful to remember that 2 MPH = 30 minutes/mile; 2.5 MPH = 25 minutes/mile; and 3 MPH = 20 minutes/mile.
Examples of dead reckoning
1. I’ve been been walking non-stop for 1:20 minutes from my last known landmark, Crystal Spring. On this kind of rolling terrain, I generally walk at around 3 MPH. I’m planning to camp at Buchanan Creek, which is 5.5 miles from Crystal Spring, per my guidebook. How much further until camp?
Using the formula Distance = Rate * Time, I calculate that I’ve walked about 4 miles (3 mph for 80 minutes). That would leave 1.5 miles to camp.
2. Today is the first of a 3-day trip with two new guys I met on an ultralight backpacking forum. Normally I walk at 3 MPH, but our pace feels much slower than that — these guys have dialed kits, but it looks as if they never actually do any hiking. A 5-mile section of easy trail takes us 2.5 hours.
Using the formula Rate = Distance / Time, I calculate that we’re walking at about 2 miles per hour, or about one-third slower than my usual hiking pace.
3. My databook says that it’s 2.5 miles between Pawnee Lake and Pawnee Pass, and I know that I normally hike at 3 MPH. Using the formula, Time = Distance / Rate, I determine that it should take me 50 minutes.
However, these two landmarks are separated by 2,500 vertical feet, and yesterday on a similarly steep section of trail I climbed at about 25 vertical feet per minute. So I adjust my expectations: rather than 50 minutes, it will take about 100 minutes (2,500 vertical feet divided by 25 vertical feet per minute).
I use an historical reference for my vertical assent speed as I have no
device to measure it. I allow time necessary to hike 1 mile for each 1000
feet of climbing. Works for me.
That’s a useful rule of thumb for accounting for vertical. Obviously it’s a starting point, and will be different for a lot of people.
If I climbed 1000 feet in 2 miles, that’d be 40 minutes + 20 minutes = 60 minutes. That equals 17 vertical feet per minute, which is a little slower than what I can actually manage (more like 25-30).
Two new guys I met on an ultralight backpacking forum— these guys have dialed kits, but it looks as if they never actually do any hiking.
Man o Man this hits home.
I never knew what “dead reackoning”, but use this mostly on my long distance hikes, usually am within 30 minutes of my estimated time of arrival, and have never used the elevation factor. What I did back home, was hike a steady pace over variable terrain (steep and flat). I used GPS to determine the distance within a few feet, and hiked the 6 mi loop a dozen times, keeping track of time. I determined my average pace from this. I did the same on flat terrain. I now use a watch with d=rt to estimate my position with good accuracy. This of course works only on established trail, and seldom cross country routes where bushwhacking and/or scrambling, and navigation are needed. I think a lot of hikers are unfamiliar with there own pace.
Example 2 is hilarious, and probably all too common.
I’m a novice backpacker, started in my 60th year, and I learn a lot from your videos, lists, etc. I think you may have saved my life a time or two! Thanks. When my husband worries, I just tell him I learned ( insert skill/info) from Andrew.
Thanks again for this great post. I wrote you earlier (in a different article) that I find it hard to estimate forward movement in time (in particular in challenging terrain) when I want to be able to do to plan/find the best camping spots before sunset. Your formula for estimating time from distinct/rate adjusted by elevation is great in theory.
The problem is application, given my lack of general experience in estimating the rate, especially in challenging terrains (e.g., walking in scree, mud, ice, climbing over felled trees, boulders and variable elevations, etc.). Other factors hindering accurate estimations include changes in encumbrance over the course of the hike (e.g., how much food & water I carry from the beginning to the end), general physical fitness levels (especially in the beginning of a hike), sleeping quality levels, and finally, averages of all these when hiking with others.
Obviously, all this can be overwhelming, so I end up sort of erroneously guesstimating (missing those great camping spots). Other times I have used rate estimations given in hiking guidebooks (e.g., Cicerone in Europe) and have found these rate predictions often times (but not always) lacking, apparently suitable for top-level hikers that practically run the trail.
It would be useful if someone (with lots of experience in groups of different physical abilities) would compose a study, estimating rates of movement with higher sensitivity to some/all of the factors I highlighted above. Maybe you know of such study/data?
Thanks again, Dan
Hi Dan –
To determine your rate, start timing yourself between points of a known distance. To calculate these distances, use a databook (available for most major trails) or measure it out beforehand in CalTopo. You can measure it on the map, too, but this usually is less precise.
All the factors you listed that affect your rate (e.g. mud, rocks, blow downs) usually average out. If there is mud in one section, you’re likely to have mud in other sections. And if you don’t, just make a small adjustment — my experience is that it’s not a dramatic difference.