Why Does My GPS Say I've Walked Further Than the Route Does?
Your GPS is not broken and your route planner is not lying. They are measuring two different things, and once you see why, the numbers stop being annoying.
It is one of the most common questions we get on the support line.
You plan an 11.8 mile walk. You do the walk. Your watch says 12.4 miles. Somebody in your group has 12.1 and somebody else has 12.6.
Nobody is wrong. Here is what is actually going on.
A route planner measures a smooth line drawn on a map. Your GPS measures a series of real positions taken while you weave, wander, stop for gates and cross ground that is never quite flat. The gap between them is usually 2 to 5 per cent, and most of it is real.
A Simple Way To Think About It
Imagine measuring a garden path.
The route planner is somebody standing at an upstairs window with a ruler, drawing a neat line down the middle of the path and measuring it.
Your GPS is somebody walking the path with a piece of string, laying it down exactly where their feet went - round the puddle, over to look at the roses, back again, and up the slope at the end.
The string is always longer. It is not a mistake. It is a more honest answer to a slightly different question.
Where the Extra Distance Actually Comes From
There are four causes, and they stack up.
1You genuinely walked further than the line
This is the biggest one, and the least discussed.
The drawn route goes down the middle of the path. You do not. You step round the boggy bit, you cross the field diagonally, you walk to the trig point and back, you overshoot the turning by thirty metres and come back.
On a day with a lot of stiles, gates, field boundaries and photograph stops, that adds up quickly.
2GPS scatter adds a little to every step
Your device fixes its position every second or so. Each of those fixes has a small error - typically a few metres in good conditions.
Because those errors are random, the recorded track wobbles slightly either side of your true path. Joining the wobbles together gives a line that is fractionally longer than the one you walked.
Modern devices smooth this out, but they cannot remove it entirely.
3Terrain and sky make it worse
This is where conditions matter enormously.
Open Cheviot moorland - somewhere like the ridge above Alwinton, with a clear view of the whole sky - is close to a best case. Your device sees plenty of satellites, the fixes are clean, and the recorded distance will be within a whisker of reality.
A steep valley is the opposite. In somewhere like Borrowdale or Great Langdale, half the sky is behind a fellside, and the signals that do reach you may have bounced off the rock first. That is called multipath, and it is the main cause of a track that looks drunk.
Dense forest - the plantation tracks in Kielder are the classic example - blocks and scatters signal from above. Tracks recorded under a heavy canopy in winter are noticeably noisier than the same route in the open.
Did you know? This is exactly what multi-band, or dual-frequency, GNSS is for. By receiving two frequencies from the same satellite, the device can identify and reject signals that have bounced. In an open field it makes very little difference. In Borrowdale it makes a big one.
4Hills, and whether your device counts them
Here is the one that surprises people.
A map measures distance flat, as if the landscape had been ironed. Walk a kilometre horizontally while climbing 300 metres, and the actual distance travelled along the ground is 1,044 metres - about 4.4 per cent further.
Most GPS devices also calculate distance in two dimensions and ignore the climb, which is why this usually is not the cause of your mismatch.
But it is worth knowing, because it explains why a genuinely steep day always feels longer than the number on your wrist suggests. On a big ascent day, you really have walked further than anything is telling you.
So Which Number Should You Trust?
| What you want to know | Trust this | Why |
|---|---|---|
| How far is this walk? | The planned route | It measures the intended line, consistently, every time |
| How far did I actually go? | Your GPS track | It measures where you really went |
| Am I on schedule at halfway? | The planned route | Your device's running total will read high, so you are further along than you think |
| Did I complete a challenge distance? | The event's official distance | Always. Never your watch |
| Comparing this week to last week | Whichever you used last time | Consistency matters more than accuracy here |
Good to know: If two people in the same group finish with different distances, neither device is faulty. They took slightly different lines, and their receivers made slightly different errors. A 2 to 3 per cent spread across a group is completely normal.
Five Things That Will Tighten Up Your Numbers
- Turn on multi-band or dual-frequency GNSS if your device has it - especially for valleys and forest. It costs battery, so use it where it earns its keep
- Let the device get a proper fix before you start walking. Standing still for thirty seconds at the trailhead prevents a messy first few hundred metres
- Use the highest sensible recording rate. Smart or variable recording saves battery but simplifies your track
- Do not compare a phone to a dedicated unit. Phones use assisted positioning and aggressive smoothing, and behave differently
- Keep the device out from under your body. A unit buried in a rucksack lid or a watch under a thick jacket cuff has a worse view of the sky than you do
When It Really Is a Problem
Small discrepancies are normal. These are not:
- A track that jumps hundreds of metres sideways in a straight line
- Distance accumulating while you are standing still
- Total distance out by more than about 10 per cent on open ground
- Elevation figures that swing wildly on a flat walk
Those point to a settings problem, a firmware issue or occasionally a hardware fault - and they are worth a conversation.
Every GPS unit and GPS watch we sell comes with our free Gold Support Package, worth £145. That includes the ability to ring somebody who has seen your exact problem before.
Frequently Asked Questions
Is my GPS watch or my route planner more accurate?
Neither, because they measure different things. The planner measures a drawn line. The watch measures the path you actually walked, which is longer. For "how far is this walk", use the planner. For "how far did I go", use the watch.
How accurate is a GPS watch for distance?
In open conditions with multi-band enabled, most modern GPS watches record distance within 1 to 3 per cent. In steep valleys or dense forest that can widen considerably, because signals bounce off terrain before reaching the device.
Why do two people on the same walk get different distances?
They walked slightly different lines, and their receivers recorded slightly different errors. Both figures are legitimate. A few per cent of difference across a group is entirely normal.
Does GPS distance include the climb?
Usually not. Most devices calculate distance horizontally and ignore the vertical component. On a steep day you have genuinely travelled further along the ground than your device reports - roughly 4 per cent further over a kilometre with 300 metres of ascent.
Will multi-band GPS fix the problem?
It will improve accuracy in difficult terrain such as valleys and forest, because it can identify signals that have bounced. In open country the improvement is marginal, and it uses more battery.
My distance seems wildly wrong. What should I do?
Check your GNSS settings and recording rate first, and make sure your firmware is current. If the track is jumping around or accumulating distance while stationary, get in touch - that is not normal behaviour.
Understanding what your GPS is telling you is half of navigating with confidence. We can teach you the other half.
Training and support are included with everything we sell - and our route planning tools are free to everyone.
GPS in the Hills - £158 2 Day GPS Courses - £225 Free OS Route Planner