Magnetic declination is the angular difference between magnetic north — where your compass needle points — and true north — the direction toward the geographic North Pole. The difference exists because the Earth’s magnetic field does not align precisely with its rotation axis, and the magnetic poles wander over time. In practical navigation, this means that a compass bearing taken from a map and applied in the field will be slightly wrong unless you correct for the local declination value.

This sounds like a technical detail. Over short distances, it effectively is. Over longer distances — a multi-hour cross-country navigation leg, a glacier crossing in whiteout, a bearing-to-bearing descent in cloud — the accumulated error becomes large enough to put you on the wrong ridge, the wrong valley, or the wrong side of a cliff. Understanding and applying declination correction is not advanced navigation — it is the baseline that makes compass bearings reliable.

Why the Compass Doesn’t Point to True North

The Earth’s magnetic field is generated by convection in the liquid outer core — a dynamic process that produces a field that is approximately, but not precisely, aligned with the planet’s rotation axis. The magnetic north pole — where compass needles point — is currently located in the Canadian Arctic, approximately 500km from the geographic North Pole. Both poles wander over decades; the magnetic north pole has moved approximately 2,300km toward Siberia since 1900 and is currently moving at roughly 50km per year.

The practical consequence is that declination values are location-specific and time-specific. The declination in central Europe today is different from what it was 20 years ago. The declination in Switzerland is different from the declination in Norway or in Colorado. Declination values printed on map margins become outdated — check the current value from an authoritative source before any serious navigation.

Current Declination Values: Where to Find Them

The most reliable source for current magnetic declination at any location worldwide:

• NOAA/NCEI World Magnetic Model: ngdc.noaa.gov/geomag/calculators/magcalc.shtml — enter coordinates for precise declination at any location, updated for the current year
• National topographic map margins: swisstopo, IGN (France), BEV (Austria) and OS (UK) all print the declination value and annual change rate on their map margins; verify whether the value is current or needs updating for elapsed years
• Navigation apps: most modern GPS apps (Gaia GPS, Maps.me) calculate and display declination automatically; the compass in these apps is already corrected

Current approximate values for key hiking regions (2025–2026)

Understanding East vs. West Declination

Declination is described as either east or west depending on whether the magnetic pole is east or west of the geographic pole from your location:

• East declination (positive): the magnetic pole is east of true north from your location; the compass needle points east of true north; to convert a map bearing (true) to a compass bearing (magnetic), add the declination value
• West declination (negative): the magnetic pole is west of true north from your location; the compass needle points west of true north; to convert a map bearing (true) to a compass bearing (magnetic), subtract the declination value

The memory aid: in Europe, declination is currently east, and is small (1–5°). In North America, declination is east in the west and west in the east — it is zero along a line called the agonic line passing roughly through the eastern US, west of which declination is east and east of which it is west. This complexity is why knowing the specific value for your location is essential rather than assuming.

Applying Declination: The Practical Method

Setting declination on an adjustable compass

Most modern baseplate compasses (Silva, Suunto, Brunton) have an adjustable declination ring — a small dial or screw mechanism that rotates the north marker on the compass housing relative to the needle. Once set to the local declination value, all subsequent bearings taken with the compass are automatically corrected — no mental arithmetic required at each bearing.

To set declination:

• Find the declination adjustment screw or dial (on the base of the compass housing or on the rotating bezel)
• Turn the adjustment until the declination marker aligns with the local declination value on the scale — east values go one direction, west values the other
• Once set, the compass reads grid north (map north) directly — the red end of the needle aligns with the adjusted north marker, not with the absolute north marker

Mental correction (fixed-bezel compasses)

For compasses without an adjustable declination mechanism:

• Determine the local declination from a map or the NOAA calculator
• When converting a map bearing to a compass bearing: if declination is east, add the value; if west, subtract
• When converting a compass bearing to a map bearing: reverse the operation
• The mnemonic: “East is least, west is best” — if declination is east (most of Europe), the true bearing from the map is less than (subtract to get) the magnetic bearing you’ll walk; if declination is west, the true bearing is more than the magnetic bearing

When Declination Matters Most

Declination correction matters most when:

• You are navigating by compass bearing in reduced visibility (cloud, mist, whiteout) over distances greater than 500m
• You are dead reckoning from a known position across featureless terrain (plateau, glacier, moorland)
• You are taking a back-bearing to confirm your position relative to a known feature
• You are using a compass to orient a map in order to identify features by direction

Declination matters less when:

• You are following a clearly marked path where the compass is used only for rough directional confirmation
• The navigation leg is short (under 200m) and the destination is visible
• You are using a GPS device that corrects for declination automatically

The discipline is knowing which situation you’re in. On a clear day following waymarked trails, declination is an interesting fact. In a whiteout on a plateau with no visible landmarks, it is the difference between finding the hut and walking over a cliff.