Convert magnetic azimuth to grid azimuth or grid azimuth to magnetic azimuth using the Grid-Magnetic angle for map bearings in degrees or mils.
Magnetic Azimuth To Grid Azimuth Formula
The following formula is used to calculate the Grid Azimuth from the Magnetic Azimuth when you know the GridโMagnetic angle (GโM angle).
Variables:
- GA is the Grid Azimuth (typically reported in degrees from 0โ360ยฐ)
- MA is the Magnetic Azimuth (typically reported in degrees from 0โ360ยฐ)
- V is the GridโMagnetic angle (GโM angle) in degrees, with east positive and west negative
To calculate the Grid Azimuth, add the Magnetic Azimuth to the GridโMagnetic angle. If the GโM angle is west (negative), this is equivalent to subtracting its magnitude from the Magnetic Azimuth. After the calculation, azimuths are commonly normalized (wrapped) to the range 0โ360ยฐ (or 0โ2ฯ radians).
Note: Magnetic declination/variation is the angle between true north and magnetic north, while the GridโMagnetic (GโM) angle is between grid north and magnetic north. On projected maps, grid north may differ from true north due to grid convergence, so declination is not always the same as the GโM angle. When needed, you can compute: GโM angle = declination โ grid convergence (using a consistent east-positive sign convention).
| Magnetic Azimuth (ยฐ) | GridโMagnetic Angle (ยฐ) | Grid Azimuth (ยฐ) |
|---|---|---|
| 0 | +10 | 10 |
| 5 | +10 | 15 |
| 10 | +10 | 20 |
| 15 | +10 | 25 |
| 30 | +10 | 40 |
| 45 | +10 | 55 |
| 60 | +10 | 70 |
| 75 | +10 | 85 |
| 90 | +10 | 100 |
| 120 | +10 | 130 |
| 135 | +10 | 145 |
| 150 | +10 | 160 |
| 180 | +10 | 190 |
| 210 | +10 | 220 |
| 225 | +10 | 235 |
| 240 | +10 | 250 |
| 270 | +10 | 280 |
| 300 | +10 | 310 |
| 315 | +10 | 325 |
| 330 | +10 | 340 |
| 355 | +10 | 5 |
| Formula: Grid Azimuth = Magnetic Azimuth + GridโMagnetic angle (east positive, west negative). Values shown assume a GโM angle of +10ยฐ (E) and the final azimuth normalized to 0โ360ยฐ. | ||
What is a Magnetic Azimuth To Grid Azimuth?
Magnetic Azimuth to Grid Azimuth is a conversion process used in navigation and mapping to relate an azimuth measured from magnetic north (the direction a compass points) to an azimuth measured from grid north (the โnorthโ direction defined by a mapโs grid lines). Because magnetic north differs from true north (magnetic declination) and grid north can differ from true north on many map projections (grid convergence), magnetic and grid azimuths generally do not align. The offset between magnetic north and grid north is the GridโMagnetic angle (GโM angle), which is used to convert magnetic azimuths to grid azimuths and vice versa.
How to Calculate Magnetic Azimuth To Grid Azimuth?
The following steps outline how to calculate the Magnetic Azimuth To Grid Azimuth.
- First, determine the Magnetic Azimuth (MA) in degrees (or radians).
- Next, determine the GridโMagnetic angle (V) in degrees (or radians). Use a positive value for east and a negative value for west (or use the E/W direction option in the calculator).
- Add the Magnetic Azimuth (MA) and the GridโMagnetic angle (V) together.
- Normalize the result to an azimuth if needed (commonly 0โ360ยฐ).
- After inserting the variables and calculating the result, check your answer with the calculator above.
Example Problem :
Use the following variables as an example problem to test your knowledge.
Magnetic Azimuth (MA) = 120 degrees
GridโMagnetic angle (V) = +10 degrees (East), so Grid Azimuth (GA) = 120ยฐ + 10ยฐ = 130ยฐ.
Preliminary Analysis: Major
– The page conflates **magnetic declination/variation (angle between Magnetic North and True North)** with the correction needed to convert **Magnetic Azimuth โ Grid Azimuth**.
– In general, converting **Magnetic โ Grid** requires the **GridโMagnetic angle (GโM angle)** (often derived from declination plus grid convergence), not simply magnetic declination/variation unless you explicitly assume **Grid North = True North**.
– The formula shown (**GA = MA + V**) is therefore not generally correct as written/defined. At minimum, it needs to define **V** as the **GridโMagnetic angle** (east/west) or clearly state the assumption that grid north and true north are the same.
– The worked/table logic ignores standard azimuth normalization (results should typically be wrapped to **0โ360ยฐ** when crossing the boundary).