Enter a latitude and longitude to see how far magnetic north is from true north, plus the dip angle and strength of Earth's magnetic field. Everything is calculated in your browser with the official World Magnetic Model 2025 coefficients.
Last updated:
Location
Decimal degrees (south negative) or degrees-minutes-seconds with N/S
Decimal degrees (west negative) or D M S with E/W
Optional; matters only for aircraft and satellites
WMM2025 covers 2025 to 2029
Optional: convert a bearing
°
Enter your values to see the result.
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How to use the Magnetic Declination Calculator
Enter your location as latitude and longitude. Use negative numbers for south and west, or type values like 40°42'46"N.
Pick the date. Declination drifts every year, so use today's date for a hike or the survey date for an old map.
Add altitude only if you are flying or working well above the ground.
Press Calculate to get the declination, the dip angle and the field strength, with the yearly change.
Convert a bearing by typing it in the optional box to get the compass bearing for a map bearing, or the reverse.
How the declination is calculated
The World Magnetic Model describes Earth's main magnetic field as a sum of spherical harmonics up to degree and order 12. That is 168 Gauss coefficients (g and h, in nanotesla) plus a yearly rate of change for each one. The calculator follows the steps in the WMM technical report:
Convert the position from geodetic latitude, longitude and height on the WGS 84 ellipsoid to geocentric spherical coordinates (radius r and geocentric latitude).
Move the coefficients to your date: g(t) = g(2025.0) + (t − 2025.0) × ġ, and the same for h.
Sum the field using Schmidt semi-normalized associated Legendre functions, which gives the north (X), east (Y) and down (Z) components.
Derive the angles: declination D = atan2(Y, X), horizontal intensity H = √(X² + Y²), total intensity F = √(H² + Z²) and inclination I = atan2(Z, H).
The yearly change shown under each value comes from evaluating the model one year later, which is exactly how the model's own secular variation works because the coefficients change linearly.
Declination at some well-known places (WMM2025, January 1, 2025)
Rounded values for sea level. Your exact result depends on the precise location and date, so use the calculator above for navigation.
Place
Declination
Inclination
Total field
New York City, USA
≈ 12.5° W
≈ 65.7°
≈ 50,900 nT
Chicago, USA
≈ 4.1° W
≈ 68.5°
≈ 52,900 nT
Miami, USA
≈ 7.2° W
≈ 53.9°
≈ 43,000 nT
Denver, USA
≈ 7.6° E
≈ 65.9°
≈ 51,200 nT
Los Angeles, USA
≈ 11.5° E
≈ 58.8°
≈ 46,100 nT
Seattle, USA
≈ 15.1° E
≈ 68.8°
≈ 52,800 nT
Anchorage, USA
≈ 14.5° E
≈ 74.0°
≈ 55,000 nT
London, UK
≈ 0.9° E
≈ 66.5°
≈ 49,100 nT
Tokyo, Japan
≈ 7.9° W
≈ 49.5°
≈ 46,800 nT
Sydney, Australia
≈ 12.8° E
≈ −64.4°
≈ 57,000 nT
Tips for hikers, pilots and surveyors
Remember the rhyme. "East is least, west is best": subtract east declination and add west declination when converting a true (map) bearing to a magnetic (compass) bearing.
Set it once. Many baseplate compasses have an adjustable declination screw. Set it to the value shown here and you can read true bearings directly.
Check old maps. Topographic maps print the declination for their survey year. Enter that year's location and today's date to see how much it has drifted since.
Stay away from metal. Cars, phones, belt buckles and fences can deflect a compass more than the model error. Take readings a few steps away.
Aviation charts use isogonic lines of magnetic variation, and runway numbers are based on magnetic headings, which is why runways are occasionally renumbered as declination drifts.
Frequently asked questions
What is magnetic declination?
Magnetic declination (also called magnetic variation) is the angle between true north, which points to the geographic North Pole, and magnetic north, where a compass needle points. It is positive (east) when magnetic north is to the east of true north and negative (west) when it is to the west.
How do I use declination with a compass?
To turn a map (true) bearing into a compass (magnetic) bearing, subtract east declination or add west declination. For example, with 10° W declination a true bearing of 90° becomes a magnetic bearing of 100°. Going from compass to map, do the opposite. The calculator does this for you in the optional bearing box.
How accurate is this declination?
The World Magnetic Model typically predicts declination to within about half a degree in most populated areas. It does not include local effects from iron-rich rocks, power lines, vehicles or magnetic storms, which can move a compass needle by a degree or more, and accuracy drops near the magnetic poles.
Why does magnetic declination change over time?
Earth's magnetic field is generated by moving molten iron in the outer core, and that flow changes slowly. As a result declination at a given place can drift by several minutes of arc per year. That is why the model is updated every five years and why old maps show an outdated declination.
What is magnetic inclination or dip?
Inclination is the angle between the magnetic field and the horizontal. It is about 0° near the magnetic equator, positive (pointing down) in the northern hemisphere and close to ±90° near the magnetic poles. Compass needles are often weighted to counter the dip for the region they are sold in.
Which model does the calculator use?
It uses WMM2025, the World Magnetic Model produced by NOAA's National Centers for Environmental Information and the British Geological Survey. It is valid from January 1, 2025 to the end of 2029, and its outputs match the official test values published with the model.
What is the blackout zone?
Close to the magnetic poles the horizontal part of the field becomes very weak. Where it is below 2,000 nanotesla, a compass cannot be trusted at all (the blackout zone), and below 6,000 nanotesla readings become unreliable (the caution zone). The calculator warns you when your location falls in either zone.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.