Coordinate Formats Explained: DD vs DMS vs DMM vs UTM, With Worked Conversions

Decimal degrees (DD), degrees-minutes-seconds (DMS) and degrees with decimal minutes (DMM) are three ways of writing the same latitude and longitude angles. UTM and MGRS are different in kind: they are grid systems that give a position in meters within a numbered zone. Here is the Washington Monument (WGS84) in each format:

The relationships are fixed: 1 degree = 60 minutes, 1 minute = 60 seconds. Converting among DD, DMS and DMM is arithmetic; converting to or from UTM requires the transverse Mercator projection formulas, so in practice it is done with a tool.

Look at where the decimal point sits and how many numbers there are:

• Decimal point right after the degrees (38.8895): decimal degrees. Usually signed (minus for south and west) and without letters.
• Three numbers per coordinate (38 53 22.2 or 38°53'22.2"): DMS. Any decimal comes after the seconds.
• Two numbers per coordinate, decimal after the minutes (38 53.370 or 38°53.370'): DMM.
• A zone number and letter followed by two large numbers in meters (18S 323478 4306483): UTM. The easting has 6 digits; the northing has up to 7.
• One run of letters and digits (18SUJ2347806483): MGRS or its U.S. civilian twin, the U.S. National Grid.

When the symbols are missing, count the numbers before the hemisphere letter. 38 53.37 N and 38 53 37 N look alike but are about 460 m apart, because the first means 53.37 minutes and the second 53 minutes 37 seconds.

DMS to DD: DD = degrees + minutes/60 + seconds/3600, then make the result negative for S or W.

Worked example, the Washington Monument latitude 38°53'22.2"N:

1. Minutes: 53 ÷ 60 = 0.883333
2. Seconds: 22.2 ÷ 3600 = 0.006167
3. Total: 38 + 0.883333 + 0.006167 = 38.889500, and N stays positive: 38.8895.

Longitude 77°02'07.1"W: 77 + 2/60 + 7.1/3600 = 77.035306; W makes it −77.0353.

DMM to DD: DD = degrees + decimal minutes/60. So 38°53.370'N is 38 + 53.370/60 = 38.8895, and 77°02.118'W is −(77 + 2.118/60) = −77.0353.

DMM to DMS: keep the whole minutes and multiply the decimal part by 60 to get seconds. 53.370' becomes 53' and 0.370 × 60 = 22.2".

A southern and eastern example, the Sydney Opera House: 33°51'24.5"S 151°12'55.1"E becomes −33.8568, 151.2153. South makes the latitude negative; east keeps the longitude positive.

Going the other way peels off whole units at each step:

1. Degrees: take the whole number part. For -77.0353, ignore the sign for now: 77°, and note the direction is W.
2. Minutes: multiply the remaining fraction by 60: 0.0353 × 60 = 2.118. The whole part is 2 minutes.
3. Seconds: multiply the remaining fraction by 60: 0.118 × 60 = 7.08. Round to 7.1 seconds.

Result: 77°02'07.1"W. For DMM, stop after step 2 and keep the decimal minutes: 77°02.118'W.

Watch the rounding. If seconds round up to 60, carry one minute; if minutes reach 60, carry one degree. Writing 59'60" is a sign of a conversion bug. Keep enough digits for the job: tenths of a second (about 3 m) or thousandths of a minute (about 1.9 m) roughly match five decimal places of a degree.

The GPS coordinate converter does these conversions in both directions and accepts most common ways of writing coordinates, including pasted Google Maps links.

UTM divides the world between 80° S and 84° N into 60 zones, each 6° of longitude wide, numbered eastward from Zone 1 at 180°–174° W (USGS Fact Sheet 077-01). Each zone is its own transverse Mercator projection with a scale factor of 0.9996 on the central meridian. Positions are in meters:

• Easting: the central meridian of every zone is assigned 500,000 m. Points west of it have smaller eastings, points east larger ones, so eastings are never negative.
• Northing: meters north of the Equator in the Northern Hemisphere. In the Southern Hemisphere the Equator is given a false northing of 10,000,000 m, so values count down toward the South Pole.

Worked example, the Washington Monument at 38.8895, -77.0353:

1. Zone: floor((−77.0353 + 180) / 6) + 1 = floor(17.16) + 1 = 18.
2. Central meridian: 18 × 6 − 183 = −75°. The monument is 2.0353° west of it.
3. Rough easting: at this latitude one degree of longitude is about 86.76 km, so the point is about 176.6 km west of the central meridian. Easting ≈ 500,000 − 176,500 ≈ 323,500 m.
4. Rough northing: 0.9996 times the meridian distance from the Equator is 4,304,514 m; the projection adds about 2 km for points this far off the central meridian.
5. Exact result from the full transverse Mercator series on the WGS84 ellipsoid: 18S 323478 mE 4306483 mN. The letter S is the 8° latitude band (32° N to 40° N).

Two more checks: Denver (39.7392, -104.9903) sits almost on the zone 13 central meridian (105° W), so its easting is 500,831 m, just 831 m east. Sydney (−33.8568, 151.2153) is in zone 56 south of the Equator, so its northing is 6,252,289 m: 10,000,000 m minus its distance south of the Equator.

To go from UTM back to latitude and longitude, use the UTM to lat/long converter. Always keep the zone number with the coordinates: the same easting and northing exist in all 60 zones.

MGRS builds on UTM and refers to exactly the same positions. The U.S. National Grid (FGDC-STD-011-2001) uses the identical numbering scheme for civilian use. A reference has three parts:

Dropping digits from each half lowers the precision, which is how MGRS references are shortened for radio or maps:

Truncate rather than round: 234 means somewhere in the 100 m square starting at 23,400 m. The polar regions above 84° N and below 80° S use the Universal Polar Stereographic (UPS) grid instead.

A few practical workflows on this site:

1. From your current location: the latitude and longitude finder gives decimal degrees, which you can then convert to DMS, DMM or UTM.
2. From an address: the address to coordinates tool geocodes a street address into decimal degrees. Check that the pin landed on the right building, because geocoders sometimes place addresses at a street segment or town center.
3. From coordinates back to a place: coordinates to address looks up the nearest known address for a point, which is a useful sanity check after any conversion.
4. Between grid and angles: use the converter tools for DD, DMS, DMM and UTM, and keep the original value alongside the converted one in your notes.

When you send coordinates to someone else, include the format and datum if there is any doubt, for example "WGS84, decimal degrees". If you are new to reading the numbers themselves, start with latitude vs longitude.

These errors account for most misplaced points:

• Treating minutes as decimals. 38°53' is 38.883°, not 38.53°. This mistake moves a point about 39 km (24 miles).
• Losing the hemisphere. Forgetting to make west longitudes negative moves the U.S. to Asia.
• Mixing DMS and DMM. 38 53.37 and 38 53 37 are different positions. Look for a third number before deciding which format you have.
• Using the wrong UTM zone. The same easting and northing exist in all 60 zones. A UTM coordinate without a zone is incomplete.
• Forgetting the southern false northing. A southern-hemisphere northing of 6,252,289 m does not mean 6,252 km north of the Equator; it means about 3,748 km south of it.
• Ignoring the datum. Coordinates from an old map on NAD27 or a national datum can be offset by tens or hundreds of meters from WGS84.
• Over-rounding. Rounding decimal degrees to three places can move a point by up to about 55 m north-south, half of a 111 m step.