Magnetic Declination Calculator
Convert between true north and magnetic north.
Apply the correct declination to your compass bearing for accurate navigation anywhere in the world.
Magnetic declination (also called magnetic variation) is the angle between true north (geographic north pole) and magnetic north (where a compass needle points). It varies by location and changes slowly over time as Earth’s magnetic field shifts.
The conversion is simple:
- Magnetic bearing = True bearing − Declination (east declination is positive, west is negative)
- True bearing = Magnetic bearing + Declination
East declination means magnetic north sits east of true north, so your compass reads lower than the true bearing. In Sydney, with about 13° east, a landmark that is truly due east at 090 reads 077 on the compass.
West declination means magnetic north sits west of true north, so your compass reads higher. In New York, with about 13° west, that same 090 true landmark reads 103.
A helpful mnemonic: “East is least, west is best”
- East declination: subtract from the true bearing to get the magnetic bearing
- West declination: add to the true bearing to get the magnetic bearing
The mnemonic runs in the direction you actually need at the map table, which is true to magnetic. Going the other way, from the compass in your hand back to the chart, just reverse both signs.
Typical declination values around the world (approximate, 2025):
| Place | Declination | Compass reads |
|---|---|---|
| Vancouver, Canada | +16° east | 16° low |
| Sydney, Australia | +13° east | 13° low |
| Moscow, Russia | +12° east | 12° low |
| London, UK | +1° east | near enough true |
| Chicago, USA | −3° west | 3° high |
| Tokyo, Japan | −8° west | 8° high |
| New York, USA | −13° west | 13° high |
| Cape Town, South Africa | −26° west | 26° high |
London is worth a note. It sat a few degrees west for most of the twentieth century, crossed zero around 2019, and is now drifting slowly east. Any British map printed before about 2015 will tell you to add for west declination, and that instruction is now the wrong way round.
Annual change: declination shifts by roughly 0.1° to 0.3° a year in most places, and faster near the poles. Charts print the value at their date of publication together with the annual rate, which is what lets you age the figure forward. A 20-year-old chart in a fast-drifting region can be 4° or 5° out, and 5° over 10 km puts you the better part of a kilometre off.
For exact current values at any location, use the World Magnetic Model (WMM) published by NOAA and the British Geological Survey.
One more trap: declination is not deviation. Declination is the planet’s field, and it depends only on where you are standing. Deviation is your own boat’s or vehicle’s ironwork pulling the needle, and it depends on which way you are pointing. Correct for both, in that order.
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This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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