Grid Convergence Angle Calculator
Computes grid convergence from latitude, longitude and the central meridian for map projections.
Enter Values
Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Enter the longitude, the zone's central meridian and the latitude.
- Press Calculate.
- Read the grid convergence angle.
How it works
Estimates grid convergence — the angle between grid north and true north — as γ ≈ (longitude − central meridian) × sin(latitude).
Worked example
1° west of the central meridian at −31.95°. Longitude 116°, central meridian 117° → γ ≈ +0.53° (grid north is rotated from true north).
Frequently asked questions
Why does grid convergence matter?
Bearings on a map grid differ from true bearings by the convergence angle; surveyors apply it when relating grid and true north.
Does grid convergence change with the date?
No. Grid convergence is pure geometry — it depends only on where you are relative to the central meridian, not on time. The angle that changes with date is magnetic declination (true north vs magnetic north); use the Magnetic Declination Calculator for that.
Related tools
- Azimuth to Bearing Converter
- UTM Zone Finder from Coordinates
- Magnetic Declination Calculator
- Combined Scale Factor Helper
- Coordinate Precision Estimator (Decimal Places to Metres)
- UTM Scale Factor Calculator
Explore more in Surveying, Coordinates, GIS & CAD.
Cite this tool
Zerdly. (2026). Grid Convergence Angle Calculator. Retrieved from https://www.zerdly.com/tools/grid-convergence-angle-calculator/
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.