Magnetic Declination Calculator

Magnetic Declination and Navigation

Magnetic declination is the angle between true north (geographic north) and magnetic north at a given location. Navigators must account for declination when converting between compass readings and map bearings.

Formulas

True to magnetic bearing:

$$\text{Magnetic} = \text{True} - \text{Declination}$$

Magnetic to true bearing:

$$\text{True} = \text{Magnetic} + \text{Declination}$$

Positive declination means magnetic north lies east of true north. Negative declination means magnetic north lies west of true north.

Practical Notes

Declination varies by location and changes slowly over time. Use current NOAA or local geomagnetic data for precise navigation. Always normalize bearings to the 0°–360° range.

Frequently Asked Questions

What is positive magnetic declination?

Positive (east) declination means magnetic north is east of true north. Subtract declination when converting true bearing to magnetic.

How do I convert a compass reading to a map bearing?

Add the local declination to your magnetic bearing to get the true bearing on the map (for east declination).

Does declination change over time?

Yes. Earth's magnetic field shifts, so declination values are updated periodically. Check current data for your area.

What is the difference between variation and declination?

They refer to the same angle. "Variation" is an older nautical term; "declination" is standard in modern navigation.

Can declination be zero?

Yes. Along agonic lines, magnetic north and true north align and declination is zero.

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Magnetic Declination and Navigation

Formulas

Practical Notes

Frequently Asked Questions

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