What is magnetic declination?

Magnetic declination (or variation) is the angle between true/grid north and magnetic north. A compass points to magnetic north, which is not the same as grid north shown on OS maps. In the UK in 2026, declination is approximately 1-2° west, meaning magnetic north is slightly west of grid north.

Grid to Mag — Add or Subtract?

In the UK with westerly declination: Grid to Mag Add, Mag to Grid Get rid (subtract). The mnemonic is: when converting FROM the grid TO the compass (magnetic), ADD westerly declination. When converting FROM compass TO grid, SUBTRACT.

Does declination change over time?

Yes. Magnetic north moves slowly over time. UK declination is currently decreasing by about 0.16° per year. Always check the declination information in the margin of your OS map, which gives the value at the date of printing and the annual rate of change.

CampCalcs

Compass Declination Calculator

Calculate magnetic declination correction for accurate compass navigation in the UK.

Grid Bearing

Enter the grid bearing

Declination

Check your OS map margin

Declination Direction

Enter the declination direction

How We Calculate This

Magnetic bearing = Grid bearing + Declination (west) or - Declination (east)

In the UK (2026), magnetic declination is approximately 1-2° west. This means you ADD the declination when converting grid bearing to magnetic bearing.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Always verify conditions and use proper safety equipment outdoors.