Magnetic to True Bearing Calculator

How it is calculated

The tool applies true = (magnetic + declination) mod 360. Magnetic bearing is the angle you read from the compass, in degrees from 0 to 360 inclusive; a value outside that range gives no result. Declination is the local angle between magnetic north and true north in degrees: enter east declination as a positive number and west declination as a negative number (for example -12.5 for 12.5° W). If the sum goes past 360 the tool wraps it back around, and if it goes below 0 it adds 360, so the answer always lies from 0 up to (but not including) 360; a magnetic reading of 360 with no declination therefore shows 0.00°. Decimal degrees are accepted, and the bearing and declination are shown to two decimals, with E or W marking the declination direction. The declination itself is not range-checked, and the tool does not look it up for your location; you must supply it from a current chart or a declination source.

Common mistakes

• Getting the sign wrong. East declination is positive and west is negative; typing a west value without the minus sign moves the answer by twice the declination in the wrong direction.
• Using this tool to go from a true bearing back to a magnetic one with the same sign. Going the other way means subtracting the declination, so enter it with the opposite sign.
• Typing degrees and minutes as one number, such as 12.30 for 12°30'. The field wants decimal degrees, so 12°30' is 12.5.
• Using an old declination value. The angle slowly changes over the years, so a value from an old map can be several degrees out.
• Entering a bearing above 360 or below 0. The tool shows no result; reduce the reading to the 0 to 360 range first. A declination typo such as 150 instead of 15 is not caught, because the declination is accepted at any size.