Runway Number Calculator (Magnetic Heading → Designator)
From magnetic heading to painted runway number and back — including why runways get renumbered as the magnetic pole strolls.
Runways are numbered to the nearest 10° of magnetic heading — and the magnetic pole's wandering really does force repainting: dozens of US runways renumber each decade, paperwork, charts and all.
Formula
⚠️ For flight planning and education only — verify with official sources and certified equipment. Not for primary navigation.
Disclaimer: This tool is for general informational and estimation purposes only and is not professional financial, tax, accounting or legal advice. All figures are estimates — verify with a qualified professional before making decisions. Read the full disclaimer.
From magnetic heading to painted runway number and back — including why runways get renumbered as the magnetic pole strolls.
About Runway Number Calculator (Magnetic Heading → Designator)
Runway 09 isn't pointing at 090 true — it's pointing within five degrees of 090 magnetic, today. This calculator does the designator arithmetic in both directions (heading to painted number, with the reciprocal end), then adds the part most pilots never compute: how close the heading sits to the rounding boundary, and — given the local rate of magnetic drift — roughly when the airport will face the repainting, re-charting bureaucratic adventure of a renumbering.
How to use Runway Number Calculator (Magnetic Heading → Designator)
- 1Enter — sensible defaults are pre-filled so you see a worked result immediately.
- 2Read the live results: .
- 3Check the "With your numbers" line to see the formula designator = magnetic heading ÷ 10, rounded (360° → 36); reciprocal = ±18 substituted step by step.
- 4Adjust inputs (or flip the unit toggle) until the scenario matches yours, then copy or share the result.
Why use Runway Number Calculator (Magnetic Heading → Designator)?
- ✓Instant, free and private — every calculation runs in your browser, nothing is uploaded
- ✓Built on the published formula designator = magnetic heading ÷ 10, rounded (360° → 36); reciprocal = ±18 with sources cited on the page
- ✓Runways are numbered to the nearest 10° of magnetic heading — and the magnetic pole's wandering really does force repainting: dozens of US runways renumber each decade, paperwork, charts and all.
- ✓Switch units, tweak any input and watch every result update live
Frequently asked questions
Why magnetic rather than true headings for runway numbers?+
Because the instrument you line up with — the compass, or the heading bug slaved to magnetometers — reads magnetic. A runway numbered to true would disagree with the DG by the local variation on every takeoff. (Exception that proves the rule: far-northern Canada numbers some runways to TRUE because converging meridians make magnetic meaningless there.)
How does a renumbering actually happen?+
When drift carries the heading past the ±5° rounding boundary, the airport authority repaints thresholds, updates signage and lighting documentation, and the change cascades: charts, approach procedure titles (an 'ILS RWY 27' becomes 'ILS RWY 28'), databases, ATIS phrasing. Oakland, Wichita and dozens more have done it this century — a purely geophysical maintenance cost.
What about parallel runways' L/C/R letters?+
Parallels share the number and split by Left/Center/Right as seen on approach (09L/09C/09R). Airports with more than three parallels cheat a number sideways: Dallas–Fort Worth's five north-south runways wear 17/18 designators despite near-identical headings — the rule bends so call signs stay unambiguous.
Is the painted number exactly my rollout heading?+
Within the rounding's ±5°, yes — check the chart's exact value (e.g., '087° magnetic' in the airport diagram fine print). For a compass/DG check on the runway it's accurate enough to catch gross errors; for setting the bug before an instrument departure, use the charted exact heading, not the paint times ten.
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