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Coordinates: DD, DM and DMS

A phone gives you a position in decimal degrees, the chart wants degrees and minutes, and older publications carry full seconds. Type the coordinates in any of those notations and get all three back; a click copies the whole pair, ready to paste into a message or a logbook.

e.g. 54.535 or 54°32.1′ or 54 32 06 N

e.g. 18.56 or 018°33.6′ or 18 33 36 E

The position loaded above is Cape Horn. Working notation at sea is DM, minutes with three decimals (0.001′ of latitude is about 1.9 m), and one minute of latitude is one nautical mile.

Frequent questions about coordinates

How do I convert degrees, minutes and seconds into decimal degrees?

Keep the degrees, divide the minutes by 60, divide the seconds by 3600 and add it all up. For example 54°31′21″ is 54 + 31/60 + 21/3600 = 54.5225°. South and West come out negative.

Which notation goes on the chart and which one comes out of a phone?

Navigation and paper charts use DM: degrees and decimal minutes (54°31.35′ N). Phones and mapping services usually give decimal degrees (DD), while older publications and surveying use full DMS. It is the same position written three ways.

Why is one minute of latitude one nautical mile?

Because the nautical mile was defined from a minute of arc of a meridian; the 1852 m adopted in 1929 is its average length. That is what lets you step off a distance straight from the latitude scale. It works for latitude only: a minute of longitude shrinks towards the poles.

How do I enter a southern or western position?

Add the hemisphere letter (S or W, before or after the number) or put a minus in front: "33°51′ S" and "-33.85" mean the same thing. N and E are the default. If you write both a minus and a letter, the letter wins.

How accurate is a decimal minute?

One thousandth of a minute of latitude is about 1.9 m, which is finer than any bridge GPS reading. Three decimals of a minute is the practice on board, and it is what this converter shows.

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