You’ve got a phone with OS maps on it, you walk on paths, and the compass in the bottom of your rucksack hasn’t come out in two years. It’s a fair question.
Yes, and for a reason most people get wrong. It isn’t that you’ll use it often. On the great majority of British hill days in decent visibility you won’t take it out at all. It’s that a compass is the only piece of kit whose entire value sits in the situation where everything else has already failed, and it weighs about thirty grams.
The catch is the bit nobody says out loud: a compass you can’t use isn’t a safety item, it’s a lucky charm. Below is what one is actually for, when you genuinely need it, and how little you have to learn to make carrying it worth anything.
What a Compass Is Actually For
Forget the survival-programme version where someone holds one up and declares which way is north. That is almost never the job.
In real hill walking a compass does three things.
1. It sets your map. Turning the map so it matches the ground is the single most useful habit in navigation, and it takes two seconds with a compass. This is the job it does most often by a wide margin, and it’s what prevents the classic 180-degree error where you set off confidently in exactly the wrong direction.
2. It lets you walk a straight line you can’t see. This is the big one. When the cloud is down and there’s no path, a bearing is the only thing that will take you from where you are to where you want to be. Nothing else in your kit does this. Not the map on its own, and not comfortably your phone.
3. It helps you work out where you are. Taking a bearing to something you can identify, or reading the direction a slope falls away, turns “somewhere on this hillside” into an actual position. Slope aspect in particular is a genuinely powerful trick on featureless ground.
If you’d like the technique rather than the argument, our guide to using a compass on a map covers it step by step.
When You Genuinely Won’t Need It
Let’s be honest about this, because pretending otherwise is how people stop trusting safety advice.
On a waymarked path, in good visibility, on a hill with people about and an obvious way back, you will not use a compass. The path is doing the navigating. That covers an enormous amount of British walking and there is nothing wrong with it.
If that’s the entirety of your walking, and you’re honest that it is, you are not in danger for want of a compass.
When It’s the Only Thing That Will Do
And here’s the other side.
When the cloud comes down on open ground. This is the scenario. No path, no landmarks, no horizon, and a need to get from here to somewhere specific. A bearing is the answer and there isn’t another one.
When the path disappears. Common on moorland and on eroded ground, where a line printed on the map stopped existing years ago.
When your phone stops. Cold, rain on the screen, a drop onto rock, or offline maps that were never actually downloaded. We’ve written honestly about whether a phone is enough, and the short version is that it’s excellent right up until it isn’t.
When you need to be sure rather than fairly confident. Before committing to a descent, for instance, where being one valley out is a long walk.
Notice that these all have something in common. They’re the situations where the consequences are highest and the alternatives are gone. That’s precisely why the thirty grams is worth it even though you’ll rarely reach for them.
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The Honest Problem: Carrying One You Can’t Use
Here’s where a lot of hill walking advice quietly fails people.
Telling someone to carry a compass, without them ever learning to use it, produces a walker who believes they have a safety net and does not. That’s arguably worse than carrying nothing, because it supports decisions, like heading onto open ground with weather coming, that they’d otherwise have thought twice about.
The good news is the bar is much lower than people assume. To get real value from a compass you need to be able to do exactly three things:
1. Set the map. Five minutes to learn.
2. Take a bearing from the map and walk it. Twenty minutes to learn, and then a handful of goes on ground where you can see the target and check yourself.
3. Read a slope’s aspect and match it to the map. Ten minutes.
That’s it. That is genuinely the whole minimum, and it’s an afternoon’s work, not a qualification. Our guide to practising navigation without getting lost is built around doing exactly this on ground where being wrong costs nothing.
The Thing Even Experienced Walkers Have Wrong
This is worth knowing, because it’s changing under everyone’s feet right now.
Magnetic north moves. For as long as anyone reading this has been walking, it sat west of grid north in Britain, and generations of walkers learned a mnemonic to adjust for it: grid to mag, add; mag to grid, get rid.
That rule is no longer safe to use. The line of zero variation has been sweeping westwards across Britain, and behind it the adjustment runs the other way. It left England at Berwick-upon-Tweed in December 2025 and is crossing Scotland during 2026. By 2040 compasses everywhere in the UK will point east of true north.
If you apply a memorised rule in the wrong direction, you don’t just lose the correction, you double the error.
Two practical points. First, the angle involved is currently very small, so for most walking it barely matters. Second, and more importantly: don’t memorise a direction, look it up. Check the current figure for where you’re actually going, note whether it’s east or west, and work from that. It takes about ten seconds. The British Geological Survey’s grid magnetic angle calculator will give you the current figure for any location in Great Britain, from a grid reference or even just a postcode.
The compass hasn’t stopped working. The shortcut has.
What to Buy
Not much of a decision, happily.
A baseplate compass with a clear plastic base, a rotating housing and a straight edge. That’s the standard walker’s compass and it’s what every UK instructional book assumes.
Romer scales on the baseplate for 1:25,000 and 1:50,000. These are the little rulers for reading grid references, and they’re genuinely useful.
Don’t overspend. A reliable compass costs less than a decent lunch. The expensive ones add sighting mirrors and global needles, which matter for precision work and for travelling outside Europe, and are not necessary for UK hill walking.
Skip the button compass on your zip pull. It’ll tell you roughly which way is north and it will not let you walk a bearing.
Once you’ve got one, it’s worth knowing how to check it’s still working, because compasses do develop faults and a reversed needle is a genuinely dangerous thing to discover in cloud.
What About the Phone Compass?
Reasonable question, and the answer is a qualified “sometimes”.
Your phone has a magnetometer, and for setting the map it’s perfectly adequate. If that’s all you’re doing, use it.
For walking a bearing, it’s poor. It’s affected by nearby metal, it needs recalibrating regularly, it’s harder to hold steadily on a line, and it depends on a battery that the cold is already working against. Following a phone arrow across open ground in poor visibility is exactly the situation where you want the thing that cannot run out.
Use the phone for convenience. Carry the compass for the day the convenience stops.
The Short Version
You will rarely use a compass. That isn’t an argument against carrying one, because its whole value lives in the situation where your other options have gone.
Carry a basic baseplate compass, and spend one afternoon learning to set the map, walk a bearing and read a slope. That’s the minimum that turns thirty grams of plastic from a lucky charm into an actual safety net.
And don’t trust the old mnemonic about which way to adjust. Look it up instead.
Frequently Asked Questions
Do I really need a compass if I have a phone?
Yes, for the same reason you carry a spare torch. Your phone is better than a compass at telling you where you are, and worse at getting you somewhere you cannot see. It also fails in predictable ways: cold batteries, wet screens, drops, and offline maps that were never downloaded. A compass needs no power and costs thirty grams. The honest test is whether you could get off the hill if the phone stopped right now.
What is a compass actually used for in hill walking?
Three things. Setting the map so it matches the ground, which is the job it does most often and which prevents the classic 180-degree error. Walking a bearing to somewhere you cannot see, which is the one thing no other item of kit can do. And working out your position, either by taking a bearing to something you can identify or by reading the direction a slope falls away.
What kind of compass should I buy for walking?
A standard baseplate compass with a clear base, a rotating housing and a straight edge, ideally with romer scales for 1:25,000 and 1:50,000 printed on it. It should cost less than a decent lunch. Sighting mirrors and global needles are for precision work and travel outside Europe, and are unnecessary for UK hill walking. Avoid button compasses on zip pulls, which cannot be used to walk a bearing.
Is the compass on my phone good enough?
For setting the map, yes. For walking a bearing across open ground in poor visibility, no. Phone magnetometers are affected by nearby metal, need recalibrating, are awkward to hold on a steady line, and depend on a battery that cold weather is already draining. That last situation is exactly the one where you want a tool that cannot run out of power.
Do I need to adjust for magnetic variation in the UK?
The angle is currently very small, so for most walking it makes little practical difference. What matters is that you should not rely on the old “grid to mag, add” mnemonic, because the direction of the adjustment has been changing across Britain and applying a memorised rule the wrong way doubles the error rather than removing it. Look up the current figure for your location and date instead.
How long does it take to learn to use a compass?
The three things that actually matter take about an afternoon between them: setting the map, taking and walking a bearing, and reading slope aspect. Making them feel automatic takes a handful of outings, ideally on familiar ground where you can see your target and check whether it worked. It is a much smaller job than most people expect.
Learn the Three Things That Matter
Carrying a compass only counts if you can use it, and the minimum is genuinely an afternoon rather than a course.
The free Digital Safety Net course is sixteen lessons on getting your phone and your planning reliable, which is the foundation that makes the compass a backup rather than a mystery. It costs nothing, and it will tell you quickly whether you want to go further.
So, honest answer: is there a compass in your rucksack, and could you use it today? Ask any questions in the comments below.
