What is degrees decimal minutes (DDM)?

DDM expresses a coordinate as whole degrees plus minutes carried to decimals, for example 51 30.500 N. It is the standard format on GPS units, marine charts, and aviation, sitting between full decimal degrees and the older degrees-minutes-seconds notation.

How do I convert DD to DDM?

Take the absolute value of the decimal degree. The whole-number part is the degrees. Multiply the fractional part by 60 to get the decimal minutes. The sign or hemisphere comes from whether the original value was positive or negative.

How do I convert DDM back to decimal degrees?

Divide the decimal minutes by 60 and add the result to the whole degrees. Then apply the hemisphere: south latitudes and west longitudes are negative in decimal degrees.

What sign conventions does this use?

North latitude and east longitude are positive. South and west are negative. The tool shows the hemisphere letter in DDM output and uses the sign in decimal output.

How precise should decimal minutes be?

Three decimal places of a minute is about 1.8 metres of latitude, which is fine for most navigation. The tool keeps enough precision that a round trip back to decimal degrees reproduces your input closely.

Decimal Degrees ↔ Degrees Decimal Minutes

Decimal degrees and degrees-decimal-minutes are the two coordinate formats you meet most often in modern navigation. GPS receivers and marine charts favour DDM, while mapping APIs and spreadsheets use plain decimal degrees. This tool converts cleanly in both directions.

How it works

The conversion is purely arithmetic. To go from decimal degrees to DDM:

degrees = floor(abs(DD))
minutes = (abs(DD) - degrees) * 60
hemisphere = DD < 0 ? (S or W) : (N or E)

To go the other way, from DDM back to decimal degrees:

DD = degrees + minutes / 60
DD = (hemisphere is S or W) ? -DD : DD

Latitude uses N and S, longitude uses E and W. North and east are positive; south and west are negative.

Tips and example

A coordinate of 51.50833 decimal degrees latitude becomes 51 30.500 N: the whole degrees are 51, and 0.50833 * 60 = 30.5 minutes. Going back, 30.500 / 60 = 0.50833, restoring 51.50833. Keep three decimal places on the minutes for roughly two-metre precision, which covers nearly all navigation and surveying preview needs.