Coordinate Converter - SVY21, UTM & Lat/Long

What it converts

This tool converts between geographic coordinates (latitude and longitude) and projected grid coordinates used in survey and setting-out work: SVY21 for Singapore, UTM in any zone, VN-2000 for Vietnam, WGS84 and Web Mercator. It converts single points or a batch pasted from a spreadsheet, and exports the result back to xlsx with a map link per point.

All of the projected systems here are Transverse Mercator with different parameters - central meridian, scale factor, false easting and northing, and the underlying ellipsoid. Getting any one of those wrong puts the point somewhere else entirely, which is why the tool names the system rather than asking you to enter raw parameters.

The mistakes that actually put a point in the wrong place

Three errors account for nearly all coordinate problems on site, and none of them produce an obviously wrong-looking number - they produce a plausible coordinate in the wrong location.

Easting and northing swapped. Most grid systems quote easting first, but some workflows and most GIS libraries expect latitude before longitude, which is northing-like. A swapped pair in Singapore or Vietnam lands in the sea or in a different province, which is at least obvious; a swapped pair in a local grid can land a few hundred metres away and look entirely reasonable.

Wrong UTM zone. UTM repeats its coordinate values in every one of its 60 zones, so a point converted with the wrong zone gives a perfectly well-formed coordinate for a location hundreds of kilometres east or west. The tool asks for the zone rather than guessing it, because guessing from the coordinate alone is not possible.

Wrong datum. WGS84 and a local datum such as VN-2000 can differ by hundreds of metres at the same nominal coordinate. A GPS reading is WGS84; a site drawing is usually on the local grid. Converting the projection without converting the datum leaves that offset in place.

Formula reference

Flattening from the ellipsoid

$f = \dfrac{a - b}{a}$

First eccentricity squared

$e^{2} = 2f - f^{2}$

Radius of curvature, prime vertical

$\nu = \dfrac{a}{\sqrt{1 - e^{2}\sin^{2}\varphi}}$

Grid easting

$E = FE + k_0\,\nu\left[A + \ldots\right]$

Grid northing

$N = FN + k_0\left[M - M_0 + \ldots\right]$

UTM scale factor

$k_0 = 0.9996$

UTM central meridian

$\lambda_0 = 6z - 183^\circ$

The full Transverse Mercator series has many more terms; the theory page gives the complete formulation. The tool evaluates the series to survey precision rather than a truncated approximation.

Assumptions and limits

A projection converts between the ellipsoid and a flat grid. It does not change datum: converting WGS84 latitude and longitude into a VN-2000 grid without the datum transformation gives a coordinate on the right projection but the wrong reference frame, and the error can be hundreds of metres. Check which datum your source data is actually on before trusting a converted value.

Transverse Mercator distortion grows with distance from the central meridian, which is why UTM is divided into zones. Converting a point far outside its proper zone remains mathematically valid but the scale distortion becomes significant for survey work.

Heights are not converted. Ellipsoidal height from GPS and orthometric height above a local datum differ by the geoid separation, which is a separate correction requiring a geoid model this tool does not include.

FAQ