Magnetic Declination Calculator
Search a place, use GPS, paste coordinates or click the map, then calculate the angle between true north and magnetic north from the British Geological Survey World Magnetic Model 2025. The page also converts true bearings to magnetic bearings.
By Aryan Khan, Founder & Editor · Updated October 2026
For example, in New York the compass needle points about 12.7 degrees west of true north in 2025 — hike a 'north' bearing uncorrected there and you drift more than 200 metres off line per kilometre.
How to use Magnetic Declination Calculator
Two norths, one correction — get the local angle:
The Magnetic Declination Calculator gives the angle between true north and magnetic north for any location, calculated from the World Magnetic Model 2025. Search a place or click the map and read the declination — plus how to convert map bearings to compass bearings.
- 1Choose a location by search, GPS, coordinates or map click.
- 2Choose a date from 2025 through 2030 and enter altitude if needed.
- 3Calculate the WMM result and review declination, inclination and field strength.
- 4Optionally enter a true bearing to convert it to magnetic bearing.
What people use Magnetic Declination Calculator for
1. Map and compass navigation
Every bearing taken from a map is true; every bearing walked is magnetic. The declination is the translation — skip it and a 5 km leg in New York ends some 1,100 m from its intended line. Pair with the Bearing Calculator for the bearings themselves.
2. Orienteering and land nav training
Courses are set in one north and walked in the other. This page supplies the local figure instructors write on the board — and explains why it expires.
3. Solar and antenna alignment
Panels and dishes are aimed by compass more often than by survey. Correct the compass with the declination or the 'south-facing' array faces south-west by twelve degrees.
4. Historic map reading
Old surveys were run on the magnetic north of their day — in parts of the US that differs from today's by several degrees. The model's current figure frames how far the old needle has wandered.
Worked examples
Declination ≈ 12.7°W (2025). Map bearing 090° (due east, true). Magnetic bearing = true − declination = 090 − (−12.7) = 102.7° — set about 103° on the compass. Walk 090 on the dial instead and you walk a line rotated nearly 13° off the map's.
Declination ≈ 11.4°E. The same true 090° becomes magnetic 090 − 11.4 = 78.6°. East declination subtracts, west adds — 'East is least, west is best' as the mnemonic has it (for converting true to magnetic).
Approximate declination, 2025 (WMM — values drift yearly)
Rounded from the World Magnetic Model — check your exact spot on the calculator, and expect roughly a tenth of a degree of yearly change in many regions.
| City | Declination (2025, approx) |
|---|---|
| New York | 12.7° W |
| Chicago | 3.5° W |
| Denver | 7.9° E |
| Los Angeles | 11.4° E |
| Seattle | 15.5° E |
| London | 0.9° E |
| Sydney | 12.5° E |
The agonic line (zero declination) currently runs through the US Midwest-to-Southeast and near the UK. London's needle pointed about 24° W in 1800, crossed true north in the mid-2010s, and now sits slightly east — declination is a moving target by design.
Magnetic declination is the angle between true north and magnetic north, and it changes over time
A compass points toward magnetic north, while maps and geodesic bearings usually reference true geographic north. Declination provides the correction between those directions at a particular place and date.
The magnetic field changes over time and local anomalies can affect compasses. Critical navigation should use a current geomagnetic model, chart or official navigation source rather than an undated planning estimate.
How to interpret the result
The most common errors come from using a correct result to answer the wrong geographic question. Keep these points in mind for Magnetic Declination Calculator:
- Include your height inputs explicitly (eye height, mast height, deck level) when sharing visibility results: the same hill answers differently for a child, an adult and a 10 m antenna, and unstated heights make numbers unreproducible.
- Treat climate and hardiness outputs as 30-year character, not this year's weather: a zone tells you what winters usually allow, and microclimates — walls, slopes, urban heat — shift a real garden half a zone either way.
Limits & appropriate use
Terrain intelligence carries one dominant limit: the model sees bare earth at ~90 m spacing with metres of vertical error, and is blind to canopies, walls and wires. Every downstream answer inherits it — profiles show terrain truth with noisy amplitude, line-of-sight verdicts are pending trees, horizons assume open ground, and solar radiation averages assume an unshaded panel. The second limit is temporal: climate letters and hardiness zones are thirty-year character, not this year's behaviour, and seismicity is a mood, not a hazard model. Each result here is printed with its recipe precisely so these boundaries travel with the number.
The value proposition is screening-grade truth at zero cost: orientation for sites, gardens, antennas, shoots and curiosity, with the upgrade points clearly marked. When money or safety attaches to the answer — tower siting, flood insurance, structural shading, avalanche terrain — the escalation is professional: licensed survey, certified shade studies, regulatory flood determinations and geological hazard services. A good free tool makes that ladder visible instead of pretending to be the top of it.
- Construction and tower siting → licensed topographic survey.
- Flood decisions → regulatory determinations (FEMA/FIRM in the US).
- Solar finance → certified shade and production studies.
Data & methodology
The browser sends the selected coordinate, altitude and date to a MapBench server route that requests the British Geological Survey WMM 2025 web service. MapBench displays model output and clearly separates it from physical compass measurements.
For source details, licences and model limitations, see Data Sources and Methodology.
Key terms worth knowing
- Köppen class
- The letter-code climate system from temperature/precipitation thresholds.
- DEM
- Digital elevation model: a grid of terrain heights, e.g. Copernicus GLO-90.
Editorial guidance: MapBench explains the method and limitations so the tool can be used as a transparent reference, not as a black-box answer. For legal boundaries, safety-critical routing, surveying, engineering, regulated decisions or official statistics, verify the result with the responsible authority or a qualified professional.
Category: Earth Science. Results are intended for everyday analysis and planning unless a page explicitly states otherwise.
What magnetic declination actually tells you
A compass points toward magnetic north, while maps and geographic bearings are usually referenced to true north. The angle between those two directions is magnetic declination, sometimes called magnetic variation. It is not a fixed number for a country or even for one city. The value depends on latitude, longitude, altitude and date because Earth's magnetic field changes both across space and through time.
That distinction matters when you compare a map bearing with a physical compass. If the model reports an easterly declination, magnetic north lies east of true north; a westerly value puts it to the west. MapBench keeps the sign convention visible and includes a direct true-to-magnetic bearing converter so you do not have to remember the arithmetic while working in the field.
Why the date is part of the input
Earth's core generates a magnetic field that evolves over time. A declination value copied from an old paper map can therefore be wrong today even when the coordinates are unchanged. The World Magnetic Model is periodically updated so navigation systems can estimate that changing field. This page uses the 2025 epoch model and deliberately limits the date picker to the model's intended 2025–2030 window rather than pretending a five-year model stays valid indefinitely.
The page also exposes inclination, or magnetic dip, and field intensity where the upstream model provides them. Those values help explain why the magnetic field is a three-dimensional vector rather than a simple horizontal arrow. For an everyday compass correction, declination is the key result; the additional field values are useful context for technical users.
Data source and calculation path
MapBench does not invent a local magnetic correction from longitude or a rough regional table. The selected coordinates, altitude and date are sent through a MapBench server route to the British Geological Survey World Magnetic Model web service. The returned model fields are then displayed in the tool. This keeps the model source separate from the user interface and makes the method auditable.
A model result is still not the same thing as a physical compass observation. Nearby steel, reinforced concrete, vehicles, power equipment, phones, speakers and local crustal anomalies can disturb a real instrument. For safety-critical marine, aviation or surveying work, follow the relevant professional navigation standard and current official notices rather than relying on a browser calculator alone.
Related MapBench tools: Bearing Calculator, Latitude & Longitude Finder, and Find My Location.
Method, assumptions & limits
- This tool’s method
- The browser sends the selected coordinate, altitude and date to a MapBench server route that requests the British Geological Survey WMM 2025 web service. MapBench displays model output and clearly separates it from physical compass measurements.
- Before relying on the answer
- Check the location, height units and any model options shown by this calculator. A terrain lookup and a geometric Earth model answer different questions.
- What the result cannot establish
- Local terrain, atmospheric conditions and source resolution can matter more than numerical rounding. Do not use a planning result for safety-critical work.
Coverage: Worldwide. Search, basemap and external data requests may use third-party services; browser-based does not mean every operation is offline. Read the source and licence notes, calculation methodology and privacy policy. If a result looks inconsistent, report a correction with the inputs and mode used.
Frequently asked questions
Clear answers about the calculation, accuracy and appropriate use.
What model does this calculator use?
MapBench requests the British Geological Survey World Magnetic Model 2025 result for the selected coordinates, altitude and date.
What does positive declination mean?
Positive declination means magnetic north lies east of true north; negative declination means it lies west.
How do I convert true bearing to magnetic bearing?
Using the common east-positive convention, magnetic bearing equals true bearing minus declination. The tool performs that conversion for you.
Can a physical compass differ from the model?
Yes. Steel, vehicles, electronics, local magnetic anomalies and instrument calibration can affect a real compass reading.
Is WMM valid forever?
No. WMM 2025 is an epoch model intended for the 2025–2030 period. Magnetic field values change over time.
Declination versus deviation?
Declination is the Earth's doing (true versus magnetic north). Deviation is your compass's local error from nearby metal, vehicles and electronics. This page prices the planet's part; the compass's part is cured by distance from iron, not by models.
Why does my hiking app show a different number?
Apps vary in model vintage (WMM updates every five years) and rounding. A few tenths of a degree between sources is normal; several degrees means one source is stale — WMM 2025 is the current edition.
Grid north — a third north?
On maps with a grid (UTM, National Grid), grid north differs slightly from true north away from the grid's central meridian — a small, printed-on-the-map correction (convergence) that careful navigators stack with declination.
Can I use a 10-year-old map's declination note?
The diagram is a museum piece: US declinations drift roughly 0.05–0.1° per year in many areas, so a decade-old figure can be a degree off — hundreds of metres on a long leg. Use the current model.
Is declination the same at altitude or underground?
The field direction varies smoothly; at aircraft altitudes the change is small for navigation purposes, but mines and surveys use local measurements where the work demands them.
The south magnetic pole?
Declination is defined worldwide by the same model — near the magnetic poles it swings wildly and compasses become useless for direction, which polar travellers plan around with grid and gyro methods.
Phone compass calibration?
Phones fuse magnetometer, gyro and GPS; their 'true north' toggle usually applies this same model internally. Knowing the local figure lets you audit the phone rather than trust it blind.
Related tools and resources
Bearings to convert: the Bearing Calculator; the far side: the Map Tunnel; grids that ignore magnets: the MGRS Converter.
More free tools
Sources, methodology & editorial trust
- ✓ Browser-first processing where supported
- ✓ External sources are documented
- ✓ No account required for public tools
- ✓ Review data sources
Calculations are documented with their assumptions, limitations and source context rather than presented as unexplained answers.
Reviewed and maintained by Aryan Khan, Founder & Editor of MapBench.
Part of our bearing & midpoint hub
Magnetic Declination Calculator sits in the bearing & midpoint cluster, alongside 17 other tools that answer neighbouring questions with different methods or datasets.
You may also need
When this answer is only part of the job, these clusters cover the next step.
Read the guide behind this tool
How to Choose a Fair Meeting Point Between Two or More Places — A practical guide to geographic midpoints, travel-time fairness and choosing a meeting location that works in the real world rather than only on a straight-line map.