Magnetic Heading to True Heading Calculator
Essential tool for pilots and mariners to calculate True Course from Compass and Magnetic data.
Enter the heading shown on your compass (0-359°)
Please enter a value between 0 and 359
Angle between Magnetic North and True North from your chart.
Local magnetic interference from your vessel/aircraft equipment.
0°
0°
0°
None
Formula: True Heading = Compass Heading + Deviation + Variation (using + for East, – for West).
Heading Visualization
Red: True North | Blue: Compass Heading
| Compass Reading | Deviation | Magnetic Heading | Variation | True Heading |
|---|
What is a Magnetic Heading to True Heading Calculator?
A magnetic heading to true heading calculator is a specialized navigation tool used by pilots, mariners, and land navigators to convert readings from a magnetic compass into “True” headings based on the Earth’s geographic poles. Because the Earth’s magnetic poles do not align perfectly with its rotational axis, and because vehicles often have internal magnetic interference, this conversion is vital for accurate course-plotting.
Using a magnetic heading to true heading calculator ensures that you account for both Variation (the difference between Magnetic North and True North) and Deviation (the magnetic error caused by the vehicle itself). Without this tool, navigation errors can accumulate, leading to significant off-course travel over long distances.
Magnetic Heading to True Heading Calculator Formula
The mathematical foundation of the magnetic heading to true heading calculator follows a standard sequence used in navigation training globally. The logic is captured by the mnemonic “Can Dead Men Vote At Elections?” which stands for:
- Compass Heading
- Deviation
- Magnetic Heading
- Variation
- True Heading
The step-by-step derivation for the magnetic heading to true heading calculator is as follows:
- MH = CH + Dev: Magnetic Heading = Compass Heading + Deviation.
- TH = MH + Var: True Heading = Magnetic Heading + Variation.
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| CH | Compass Heading | Degrees (°) | 0 – 359 |
| Dev | Deviation (E is +, W is -) | Degrees (°) | 0 – 15 |
| Var | Variation (E is +, W is -) | Degrees (°) | 0 – 180 |
Practical Examples (Real-World Use Cases)
Example 1: Aviation Flight Planning
A pilot flying a Cessna 172 notes a compass heading (CH) of 090°. The aircraft’s deviation card indicates a 2° West deviation for this heading. The sectional chart shows a 12° East variation for the current region. Using the magnetic heading to true heading calculator logic:
MH = 090 – 2 = 088°
TH = 088 + 12 = 100°. The true heading is 100°.
Example 2: Maritime Coastal Navigation
A boat captain sees 240° on the ship’s compass. The deviation is 3° East. The local variation is 5° West. The magnetic heading to true heading calculator computes:
MH = 240 + 3 = 243°
TH = 243 – 5 = 238°. The true heading is 238°.
How to Use This Magnetic Heading to True Heading Calculator
- Enter your current Compass Heading in the first field.
- Input the Magnetic Variation found on your navigation chart or map. Be sure to select East or West.
- Input the Magnetic Deviation specific to your vehicle/aircraft (usually found on a deviation card).
- The magnetic heading to true heading calculator will automatically display the True Heading in real-time.
- Check the “Visualizer” to see the relative difference between your Compass Heading and True North.
Key Factors That Affect Magnetic Heading to True Heading Calculator Results
When using a magnetic heading to true heading calculator, several external and internal factors influence the final data:
- Geographic Location: Variation changes as you move across the Earth’s surface. A magnetic heading to true heading calculator must use current local variation.
- Time (Annual Change): The Earth’s magnetic field shifts annually. Charts usually list the rate of change to adjust variation.
- Electronic Equipment: New avionics or radios installed in a cockpit can change the Deviation, requiring a new “compass swing.”
- Local Anomalies: Large iron deposits in the ground can cause local magnetic disturbances not accounted for by standard variation.
- Magnetic Storms: Solar activity can temporarily disrupt the Earth’s magnetic field, affecting the accuracy of the magnetic heading to true heading calculator.
- Vessel Load: In maritime contexts, shifting large metallic cargo can alter the vessel’s magnetic signature and deviation.
Frequently Asked Questions (FAQ)
1. Why is East variation added and West variation subtracted?
This is a mathematical convention. East variation means Magnetic North is to the East of True North, effectively shifting the scale. When going “From Compass to True,” we add East (Least is West, Best is East).
2. What is the difference between Heading and Course?
Heading is where the nose of the vessel is pointed. Course is the intended path over the ground. A magnetic heading to true heading calculator handles the orientation, not the wind/current drift.
3. How often should I update variation data?
Variation should be updated using the most recent charts available, as it shifts slightly every year.
4. Can this calculator be used for land hiking?
Yes, though hikers typically ignore deviation because they aren’t inside a metal vehicle. They use the magnetic heading to true heading calculator primarily for variation.
5. What if my result is over 360 degrees?
The magnetic heading to true heading calculator automatically wraps values. For example, 370° becomes 010°.
6. Does altitude affect variation?
Generally, no. Magnetic variation is a horizontal component and remains consistent for most flight altitudes within the atmosphere.
7. What is a “Compass Swing”?
It is a procedure to calibrate a compass and determine the Deviation values for the deviation card used in your magnetic heading to true heading calculator.
8. Is True North the same as Grid North?
No. True North points to the pole. Grid North refers to the map’s grid lines. They are close but usually have a small “grid convergence” difference.
Related Tools and Internal Resources
- Magnetic Variation Calculator – Determine local magnetic variation based on your GPS coordinates.
- Compass Heading Calculator – Convert True Course to Compass Heading for flight planning.
- Dead Reckoning Calculator – Calculate your position based on heading, speed, and time.
- Wind Correction Angle Calculator – Factor in wind speed to find your required heading.
- Nautical Distance Calculator – Measure distances between waypoints on a true heading.
- Aviation Fuel Calculator – Estimate fuel burn based on your calculated flight time.