Does switching from miles to kilometres change your hike distance?
No â and the confusion is entirely arithmetic, not measurement. A route is recorded once, as a sequence of GPS points, and that sequence does not change no matter which unit you look at it through afterwards. What changes is only the number printed on screen, converted from the same underlying distance. The part that catches people out is that miles and kilometres do not convert into each other along a clean ratio, so a distance that looks tidy in one unit almost never looks tidy in the other.
The short answer
Switching the unit setting on a hiking app does not remeasure, recalculate, or otherwise touch the recorded route. Distance is worked out once, from the sequence of GPS points logged during the walk, and that figure sits behind the display regardless of which unit is showing on screen. Kilometres and miles are both just that one number, converted and rounded for display. Toggle the setting and you get a different label and a different rounded figure â the walk itself, and the data describing it, has not moved.
What the unit setting is actually doing
A unit preference is a display instruction, not a recording instruction. It tells the app which conversion to apply and which word to print next to the number â kilometres or miles for distance, the matching pace per kilometre or per mile alongside it. None of that touches the GPS points a route is built from, which is why switching the setting works the same way on a hike recorded a year ago as on one you finished five minutes ago: there is nothing to redo, only a different label being applied to a number that was already sitting there.
Why a round number in one unit looks odd in the other
A mile is 1.60934 kilometres â not 1.5, not 2, not any other convenient fraction. That awkward figure is the whole reason the same walk can look tidy in one unit and messy in the other. The two systems were never designed to line up: one grew out of the metric system, the other out of an older system of measurement, and nobody reconciled them into a clean ratio afterwards.
- 10.00 km â 6.21 mi
- 5.00 km â 3.11 mi
- 5.00 mi â 8.05 km
- 10.00 mi â 16.09 km
- 1.00 mi â 1.61 km
A hike that comes out to a perfectly round number in kilometres will, in the near-total majority of cases, land on a decimal in miles, and the reverse is just as true. There is no distance, short of vanishingly rare coincidences, that converts cleanly in both directions at once. A route that looks odd after switching units has not lost precision â it has simply run into the one conversion factor that never behaves.
The same flip shows up in pace, for the same reason
Pace is reported per kilometre or per mile, so it converts along the same awkward ratio distance does. A pace that reads as a clean number of minutes per kilometre will not usually read as a clean number of minutes per mile, and vice versa. This is a different effect from the reason pace and speed point in opposite directions as you go faster, which is a matter of which way the fraction runs rather than which unit it is measured in â covered on its own in the guide to pace versus speed on a bike ride. Both end up looking slightly odd on screen for a related reason: the number shown is a converted, rounded version of one true measurement, not the measurement itself.
Things that trip people up
- Assuming a decimal distance is somehow less precise than a round one â a hike that reads 6.21 mi is exactly as precisely recorded as one that reads a clean 10.00 km. They are the same walk, described in two different units.
- Checking the map after switching units, expecting the line to have moved â it has not. Only the number and the unit label next to it changed.
- Comparing a total kept in kilometres against a total kept in miles without converting one of them first â the two figures are not directly comparable until they share a unit.
- Treating a small mismatch between a rough mental conversion and the number on screen as an app error â a quick shortcut conversion is not the same arithmetic as multiplying by 1.60934, and the two drift further apart the longer the distance gets.
Where TrailCam fits in
TrailCam reports distance and pace in kilometres or miles, whichever you prefer, and the choice applies the same way to a route recorded a year ago as to one you just finished â nothing about the underlying track changes when you switch it. Elevation gain is drawn as a profile under the map for every route regardless of which distance unit is selected. TrailCam is free to download.
Questions
- Does switching units re-record or re-measure my hike?
- No. It changes only how the same recorded distance is converted and displayed. The GPS points a route is built from are not touched by a display setting.
- Why does a round number in kilometres turn into a decimal in miles?
- Because a mile equals 1.60934 kilometres, a ratio with no clean fraction behind it. A distance that lands on a tidy number in one unit will very rarely also land on a tidy number in the other.
- Do old hikes update to a new unit too, or only ones recorded after I switch?
- A unit setting is applied whenever a route is displayed, not baked in at the moment it was recorded, so a hike from last year reads in the new unit exactly the same way a hike from this morning does.
Recording your own routes
TrailCam is an iPhone app that records your route with GPS, keeps video clips, photos and voice notes pinned to the spot where you took them, and exports the result as GPX 1.1 or CSV. It is free to download.