Formulas
One degree is 60 arcminutes and one arcminute is 60 arcseconds. To go from DMS to decimal degrees: DD = D + M ÷ 60 + S ÷ 3600.
To go the other way, the whole part is the degrees. Multiply the remaining fraction by 60: the whole part is the minutes. Multiply that fraction by 60 again to get the seconds.
Worked example
40.446195°: the degrees are 40. 0.446195 × 60 = 26.7717, so the minutes are 26. 0.7717 × 60 = 46.302, so the seconds are 46.30″ to two decimals. The result is 40° 26′ 46.30″ N as a latitude.
Going back, 40 + 26 ÷ 60 + 46.302 ÷ 3600 = 40.446195°. A longitude of −73.9857° becomes 73° 59′ 8.52″ W.
Signs, hemispheres and rounding
Signed decimal degrees use positive values for north and east and negative values for south and west. Latitude must be within ±90° and longitude within ±180°; plain angles have no limit.
Rounding the seconds can reach 60. The calculator rounds on a whole grid of seconds first, so 10.9999999° shows as 11° 0′ 0.00″ rather than 10° 59′ 60.00″.