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Adjust a compass for declination

Adjusting for declination lets you translate between the magnetic north your compass needle follows and the true north used as a map reference. Use it when transferring bearings between your map and the ground. An adjustable compass can build in the correction; a nonadjustable compass requires you to correct bearings yourself. Check which north reference your map uses: grid north can differ from true north and may require a separate correction.

Navigation 10 min practice Beginner Use this skill wherever you navigate with a map and compass, especially when moving into a different region. Make adjustments and checks on a stable surface away from vehicles, metal equipment, magnets, and electrical interference.

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Topic summary

Key takeaways

Your recorded declination includes its value, east or west direction, location, and date.
Your adjustable compass shows the intended offset, or your manual calculation uses the correct conversion direction.
The oriented map agrees with identifiable terrain without forcing the magnetic needle to follow grid north.
Repeated landmark checks agree without applying a second declination correction.
Avoid: Using an old diagram without checking its date gives you an outdated correction; confirm the current value for your exact area.
Avoid: Choosing the wrong east or west setting shifts your bearings the wrong way; verify the direction before adjusting.

Intended uses

Navigation skill (Beginner, ~10 min practice)
Requires: Baseplate compass, with its adjustment tool if required, Map of your area with north-reference information, Internet-connected device for checking current declination, if available

Climate suitability

Use this skill wherever you navigate with a map and compass, especially when moving into a different region. Make adjustments and checks on a stable surface away from vehicles, metal equipment, magnets, and electrical interference.

Andrew Skurka — Adjust for Declination & Orient a Map Watch on YouTube

Safety: Check your compass against identifiable terrain before committing to a route, particularly near cliffs, steep slopes, or water crossings. If the map, compass, and terrain disagree, stop somewhere safe and resolve the mismatch before continuing.

Required tools

Baseplate compass, with its adjustment tool if required
Map of your area with north-reference information
Internet-connected device for checking current declination, if available

Required materials

Paper for recording the declination and bearing calculations
Pencil for marking notes

Step-by-step

Find the declination value for your area on your map's declination diagram or at magnetic-declination.com.
Why: 1. Find the declination value for your area on your map's declination diagram or at magnetic-declination.com. You need a local, current value because declination changes over time and between regions; check the diagram's date and use a current lookup if it is outdated.
Determine whether the declination is east or west of true north.
Why: 2. Determine whether the declination is east or west of true north. The direction tells you which side of true north magnetic north lies on, so treating an east value as west applies the correction in the wrong direction.
On an adjustable compass, turn the declination screw until the orienting arrow matches the printed declination offset.
Why: 3. On an adjustable compass, turn the declination screw until the orienting arrow matches the printed declination offset. Follow your compass's instructions to set the specified east or west offset on its declination scale, because adjustment mechanisms and markings vary.
If your compass is not adjustable, add east declination to your magnetic bearing or subtract west declination.
Why: 4. If your compass is not adjustable, add east declination to your magnetic bearing or subtract west declination. This converts a magnetic bearing to a true bearing; reverse the arithmetic when converting a true map bearing to a magnetic bearing, keeping results within 0–359 degrees.
Double-check by orienting the map: the compass needle should align with the map's north-south grid when the map is rotated correctly.
Why: 5. Double-check by orienting the map: the compass needle should align with the map's north-south grid when the map is rotated correctly. Correction: the needle points to magnetic north, so it generally should not align directly with the grid; align the compass's north reference with the corresponding map reference and rotate the map until the needle sits in the properly corrected orienting arrow.

Tip: Declination changes slowly over years and sharply across regions. Always use a current value for the exact area you're in.

Common mistakes

Using an old diagram without checking its date gives you an outdated correction; confirm the current value for your exact area.
Choosing the wrong east or west setting shifts your bearings the wrong way; verify the direction before adjusting.
Applying manual arithmetic after setting an adjustable compass corrects the same bearing twice; use only one correction method.
Adding east declination when converting a true map bearing to magnetic reverses the conversion; subtract east or add west for that direction.
Treating grid north as true north introduces another error; use the map's grid-to-magnetic relationship when working from grid lines.

Troubleshooting

If the needle changes direction when you move your equipment, then move away from possible interference and repeat the reading.
If you cannot identify the declination screw or scale, then consult the compass instructions and use manual correction rather than guessing.
If your check disagrees with a known landmark, then verify your location, north reference, declination direction, and whether you corrected twice.
If a calculated bearing is negative or reaches 360 degrees, then add or subtract 360 degrees to put it within 0–359 degrees.

Field practice drill

At a safe location with identifiable landmarks, spend about ten minutes checking the local declination and identifying your map's north reference. Set your adjustable compass, or write down both manual conversion rules. Take a bearing to a known landmark, translate it to the map's reference, and check it against the line from your known position to that landmark. Repeat with another landmark, then orient the map and check that the surrounding features line up.

Indicators of success

Your recorded declination includes its value, east or west direction, location, and date.
Your adjustable compass shows the intended offset, or your manual calculation uses the correct conversion direction.
The oriented map agrees with identifiable terrain without forcing the magnetic needle to follow grid north.
Repeated landmark checks agree without applying a second declination correction.

Related outdoor skills

Educational reference only. Wilderness conditions change fast — practice in low-stakes settings, take a certified wilderness first-aid course, and confirm regional regulations before you rely on any of these skills in the field.