Distance to the Greenwich Meridian

Distance to the Greenwich meridian

The east-west distance from a point on Earth to the Greenwich meridian (0° longitude) is d = |longitude| × 111.32 × cos(latitude), with longitude in degrees and the result in km. The factor 111.32 km/° is the length of one degree of longitude at the equator. At higher latitudes, meridians converge, so the same longitude difference covers fewer kilometers. Example: São Paulo (-46.6°W, -23.5°S) → 46.6 × 111.32 × cos(23.5°) ≈ 4,770 km west of Greenwich. At the equator (latitude 0°), the distance is simply longitude × 111.32. At the poles, cos(90°) = 0, so all meridians converge to a single point and the distance collapses to zero.

Applications

Navigation and dead reckoning, time-zone planning (1 hour = 15° of longitude ≈ 1,668 km at the equator, but only ~830 km at latitude 60°), flight-route planning, and any analysis where east-west separation needs to be converted from degrees of longitude into kilometers on the ground.

FAQ

Why does the distance shrink toward the poles? Meridians are great circles that meet at the poles, so the parallels (east-west circles) shrink with the cosine of latitude.

Is this the same as the Haversine distance? No — this assumes you travel along a parallel at constant latitude. Haversine gives the shortest great-circle path, which curves toward the pole over long east-west spans.

Why 111.32 km/°? Earth's equatorial circumference is ~40,075 km divided by 360° ≈ 111.32 km per degree.