Using the converter
Paste a coordinate in any of the three formats and all three come back, each with its own copy button. It reads what people actually paste, with or without the degree sign, lowercase n and w, a comma or a space between the halves, letters before or after the numbers, and minus signs instead of letters. `n32 42.123 w117 09.456`, `32.70205, -117.1576` and `32°42′07.38″N 117°09′27.36″W` all give the same answer.
It checks the numbers mean something. Minutes and seconds have to be under 60, latitude within 90° and longitude within 180°, and the error says which part is wrong.
Under the result are links to open the point in your phone's map app, OpenStreetMap or Google Maps. The conversion itself happens on your device; the coordinates leave it only if you tap one of those links.
The three formats
Geocaching listings use **DDM**, degrees and decimal minutes, as in `N 32° 42.123 W 117° 09.456`, and handheld GPS units can be set to show it. Web maps and spreadsheets use **DD**, decimal degrees, as in `32.70205, -117.1576`, with south and west written as negative numbers. **DMS**, degrees, minutes and seconds, is the oldest of the three and the most to type.
Moving between them is division by 60. 42.123 minutes is 42.123 ÷ 60 = 0.70205 of a degree, so N 32° 42.123 is 32.70205°. Going the other way, the 0.123 of a minute left over is 0.123 × 60 = 7.38 seconds.
How precise the digits are
A degree of latitude is about 111 km. A thousandth of a minute, the last digit of a geocaching coordinate, is about 1.85 m north to south. East to west it shrinks with the cosine of the latitude: about 1.56 m at San Diego's 32.7° and 1.14 m at 52°.
So the converter rounds DDM to three decimal places of a minute, DD to six decimal places (11 cm) and DMS to hundredths of a second (31 cm). That's finer than the receiver can tell. GPS.gov puts a smartphone's accuracy at about 4.9 m under open sky, and worse under trees.
The missing minus sign
Drop the minus from `32.70205, -117.1576` and the point moves from San Diego to the other side of the world, in Anhui province, China. Decimal degrees carry the hemisphere in the sign alone, so a lost character costs a hemisphere. DDM spells it out with N, S, E and W, one reason puzzle owners prefer it. When a converted point lands in the sea, check the signs first.
Questions
Which format does geocaching use?
Degrees and decimal minutes, like N 32° 42.123 W 117° 09.456. Copy the DDM row to enter a coordinate on a cache page or a checker.
Why is my longitude negative?
In decimal degrees, west of Greenwich and south of the equator are negative. -117.1576 is the same as W 117.1576°.
Can I paste lowercase letters or skip the degree sign?
Yes. Letters can be either case, before or after the numbers, and the degree sign, minute and second marks are optional.
Does it work offline?
Yes, once the page has loaded. Only the map links need a connection, and they're only used if you tap one.
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