True vs Magnetic North

Part of Navigation Without Technology

Your compass does not point to true north. Understanding the difference between magnetic north and true north can prevent navigation errors of 20 degrees or more — enough to miss a target by kilometers over a day’s travel.

The Problem

The Earth has two “norths.” True north (geographic north) is the fixed point where the planet’s rotational axis intersects the surface — the top of the world on any globe. Magnetic north is where your compass needle points, and it is a different location entirely. As of the mid-2020s, the magnetic north pole sits in the Canadian Arctic, roughly 500 km (310 miles) from the geographic pole. It moves about 50-60 km per year and has been accelerating toward Siberia.

The angular difference between true north and magnetic north, measured from your specific location, is called magnetic declination (or magnetic variation). Depending on where you are, this angle can be anywhere from 0 degrees to over 25 degrees east or west. If you ignore it, your compass heading will carry a consistent error that accumulates with distance.

Over 10 km of travel, a 15-degree declination error puts you 2.6 km off course. Over 30 km, you are nearly 8 km from where you intended to be. In dense forest or featureless terrain, that is the difference between finding your destination and walking past it entirely.

How Declination Works

Imagine standing at your location and drawing one line toward geographic north (using Polaris or a shadow stick at solar noon) and another line in the direction your compass needle points. The angle between those two lines is your local declination.

• East declination means magnetic north is east of true north. Your compass needle points to the right of true north.
• West declination means magnetic north is west of true north. Your compass needle points to the left of true north.

Declination by World Region

These are approximate mid-2020s values. Declination changes slowly over years (secular variation), so these remain useful for at least a decade.

Region	Approximate Declination	Direction
Eastern United States	5-15 degrees	West
Western United States	10-18 degrees	East
Central Europe	0-5 degrees	East
United Kingdom	0-3 degrees	West (decreasing toward 0)
Eastern Siberia	5-15 degrees	West
Eastern Australia	8-13 degrees	East
Western Australia	0-5 degrees	West
Southern Africa	15-25 degrees	West
Brazil	15-22 degrees	West
Alaska	10-25 degrees	East
Agonic line (zero declination)	0 degrees	Runs roughly through the US Midwest, down through Central America

Local Anomalies

Iron ore deposits, volcanic rock, and underground mineral veins can create local magnetic anomalies that distort your compass by 5-30 degrees independently of regional declination. If your compass suddenly gives readings that contradict the sun, stars, or terrain, suspect a local anomaly. Move 500 meters and try again.

Measuring Your Local Declination

In a post-collapse scenario, you will not have access to declination charts or websites. You need to measure it yourself. Here is how.

Method 1: Polaris Comparison (Most Accurate)

Requirements: Clear night sky, Northern Hemisphere, functioning compass.

1. Locate Polaris using the Big Dipper’s pointer stars (see Navigation Without Technology).
2. Face Polaris directly. You are facing true north within about 0.7 degrees.
3. Without moving your body, look at your compass. Note where the compass needle points relative to Polaris.
4. The angle between the compass needle and your Polaris sightline is your local declination.
5. If the needle points to the right of Polaris, your declination is east. If it points to the left, your declination is west.

Accuracy: Within 2-3 degrees if you sight carefully.

Method 2: Solar Noon Shadow Stick

Requirements: Sunny day, stick, flat ground, compass.

1. Set up a shadow stick on flat ground (see the shadow stick method in the parent article).
2. At solar noon — the moment the shadow is at its shortest — the shadow points exactly true north (Northern Hemisphere) or true south (Southern Hemisphere).
3. Compare this true-north line with your compass reading at the same location.
4. The angular difference is your declination.

Finding solar noon: Solar noon is not 12:00 on a clock (even if clocks still work). It is the moment the sun reaches its highest point. Track the shadow from mid-morning — when it stops shortening and begins to lengthen, that moment is solar noon and the shortest shadow points true north/south.

Accuracy: Within 3-5 degrees. Improves if you track the shadow over a longer period.

Method 3: Sunrise/Sunset Averaging

Requirements: Clear horizon at sunrise and sunset, compass.

1. On the equinox (around March 20 or September 22), the sun rises due east and sets due west. Take compass bearings on both sunrise and sunset positions.
2. Average the two bearings. The deviation of this average from true east (90 degrees) or true west (270 degrees) approximates your declination.
3. At other times of year, this method is less accurate because the sun rises and sets north or south of due east/west depending on season and latitude.

Accuracy: 5-10 degrees. Use only as a rough check.

Applying Declination Corrections

Once you know your declination, you need to convert between compass (magnetic) bearings and true bearings. Two simple rules:

East Declination (Magnetic North Is East of True North)

• Compass to true: Subtract the declination from the compass reading.
• True to compass: Add the declination to the true bearing.

Example: Your compass reads 45 degrees. Local declination is 12 degrees east. True bearing = 45 - 12 = 33 degrees true.

West Declination (Magnetic North Is West of True North)

• Compass to true: Add the declination to the compass reading.
• True to compass: Subtract the declination from the true bearing.

Example: Your compass reads 45 degrees. Local declination is 10 degrees west. True bearing = 45 + 10 = 55 degrees true.

The Memory Aid

East is least, West is best. East declination: subtract (least) from compass to get true. West declination: add (best) to compass to get true.

Or more precisely: to go from magnetic to true, add west declination and subtract east declination.

Building a Declination Reference Tool

If you are establishing a permanent settlement, create a physical declination reference:

Step 1: Establish a True North Marker

On a clear night, drive two stakes into the ground aligned precisely with Polaris. These stakes now define a true north line that works day or night.

Step 2: Mark the Magnetic Bearing

Stand at the southern stake and take a compass reading along the line to the northern stake. The difference between this reading and 360/0 degrees (north) is your declination.

Step 3: Create a Correction Board

Carve or scratch a protractor-like arc on a flat board or stone slab. Mark true north and magnetic north as separate lines, with the declination angle clearly labeled. Anyone in your group can use this board to quickly convert bearings.

Step 4: Update Annually

Declination changes over time (secular variation). Re-measure using Polaris once a year and update your correction board. The change is small — typically 0.1-0.2 degrees per year — but over a decade it adds up.

When Declination Does Not Matter

Not every navigation task requires declination correction:

• Following a back-bearing. If you walked out on a compass bearing of 120 degrees and want to return, just follow 300 degrees (120 + 180). The declination error is the same in both directions and cancels out.
• Navigating between visible landmarks. If you can see your destination, you do not need a bearing at all.
• Relative bearings. If you are mapping your local area with compass and paces, and all bearings use the same uncorrected compass, the relative angles between features are correct. The whole map is just rotated by the declination angle — which does not matter for local use.
• Small distances. Over distances of less than 1 km, even a 15-degree error puts you only 260 meters off course. In open terrain, that is still within visual range of the target.

When Declination Is Critical

• Long-distance travel through featureless terrain (desert, plains, dense forest) where you cannot see your destination.
• Coordinating with others using a shared map or agreed-upon bearings. If one person corrects for declination and another does not, they will diverge.
• Using old maps that reference true north. Pre-collapse topographic maps use true north for their grid. If you navigate with a compass without correcting, you will steadily drift off the map’s grid.
• Triangulation and position fixing. Errors in individual bearings multiply when combining two or three bearings to fix a position (see Map Making).

Magnetic Dip (Inclination)

A related phenomenon that affects improvised compasses: the Earth’s magnetic field is not horizontal. In most locations, the field lines angle downward into the Earth. This is called magnetic dip or inclination.

• At the magnetic equator, the field is roughly horizontal (0 degrees dip).
• At the magnetic poles, it plunges straight down (90 degrees dip).
• In most of North America and Europe, dip is 60-75 degrees.

This matters because a magnetized needle, when balanced at its center, will try to tilt downward following the field lines. In a floating compass this is not a problem — the water keeps the needle horizontal. But in a suspended compass or a pivot compass, the needle may tilt noticeably and stick. Solutions:

• Balance the needle slightly off-center so gravity counteracts the dip.
• Add a small counterweight (a dab of wax or mud) to the north-dipping end (in the Northern Hemisphere).

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Key Takeaways

1. Magnetic north and true north are not the same place. The difference (declination) ranges from 0 to 25+ degrees depending on your location.
2. Measure your local declination by comparing Polaris (true north) to your compass reading. Do this once and record it.
3. Apply the correction consistently: “East is least, West is best” — subtract east declination, add west declination when converting compass to true.
4. For back-bearings, short distances, and local mapping, declination correction is unnecessary. For long-distance travel and map coordination, it is essential.
5. Magnetic dip causes compass needles to tilt in pivot or suspended designs. Floating compasses are immune to this problem.