Which coordinate format should I give 911 dispatch?

Decimal degrees (for example 40.712800, -74.006000) on the WGS84 datum is the easiest to dictate by phone and the format phone compass apps display. Trained search-and-rescue teams with a map may prefer UTM or MGRS. Always state the datum first.

Does GPS work without phone signal?

Yes. The GPS receiver computes position directly from satellites with no cellular coverage, so offline GPS apps and even many compass apps can show your coordinates in airplane mode. What fails without service is calling or texting — that is why satellite messengers and PLBs matter in remote terrain.

What is the difference between UTM and MGRS?

UTM describes a point as zone plus easting and northing in metres (18N E 583959 N 4507351). MGRS wraps the same WGS84 position into a zone, latitude band, 100 km square and a compact grid string (18TWL8395907351) that is easier to read aloud and mark on a military/USNG-style map.

Why must I state WGS84?

The same numeric grid on a different datum (NAD27, ED50 and many local datums) can be displaced by tens to hundreds of metres. Telling dispatch 'WGS84' makes the coordinate unambiguous; the four formats produced here are all computed on WGS84.

Are my coordinates sent to a server?

No. Every conversion runs locally in your browser using published USGS/NGA map-projection mathematics. The tool works fully offline once the page has been cached.

Handheld GPS and paper topographic map with marked coordinates on a rocky summit

Rescue Coordinate Converter救援坐标转换器

DD ↔ DMS ↔ UTM ↔ MGRS on WGS84, computed fully offline — with copy-ready text to read to emergency dispatch. WGS84 下 DD ↔ DMS ↔ UTM ↔ MGRS 完全离线互转，一键生成可直接念给救援调度的标准文本。

🧭 Weather & Navigation天气与导航求救 📍 WGS84 · SAR-readyWGS84 · 搜救即用 📅 Updated Oct 20262026 年 10 月更新

Four ways to say the same point

A position on Earth is only useful in a rescue if the person on the other end of the phone uses the same language — the same coordinate format and the same datum. This tool converts between the four formats rescuers actually use, all on the WGS84 datum, entirely inside your browser.

Decimal degrees (DD) writes latitude and longitude as signed numbers — 40.712800, -74.006000. It is the format phone compass apps display and the easiest to dictate by phone. Degrees-minutes-seconds (DMS) splits each value into 40°42′46.08″N 74°00′21.60″W, common on paper maps and older GPS screens. UTM projects the globe into 6° zones and measures metres from a central meridian and the equator — 18N E 583959 N 4507351 — so distances on a map can be read with a ruler. MGRS compresses the same UTM point into a zone, latitude band, 100 km square and a grid string: 18TWL8395907351, where five trailing digits per axis pin the point to roughly one metre.

The mathematics

Conversions use the WGS84 ellipsoid (semi-major axis 6 378 137 m, flattening 1/298.257223563). Geographic-to-UTM and UTM-to-geographic are evaluated with the USGS Professional Paper 1395 Krueger-series equations; MGRS lettering follows the NGA Universal Grids standard (NGA.STND.0037). Round-tripping a point through UTM or MGRS at five-digit precision returns to within about half a metre — comfortably inside the accuracy of a consumer phone GPS in open sky, which is roughly 3–10 m.

Reporting your position to dispatch

Call the local emergency number (911 in the USA and Canada, 112 across the EU and most of the world, 120 in China), stay on the line and open with the datum: “I am on WGS84.” Give decimal degrees for a phone-only dispatcher, or UTM/MGRS if they have a map. Add a nearby landmark, trail or drainage name, the time of the reading, your party size and any injuries. State the datum because older maps and legacy units use NAD27, ED50 or local datums; identical numbers on different datums can be hundreds of metres apart.

同一个点，四种报法

救援中，只有当电话那头与你使用同一套「坐标语言」——相同的格式与相同的基准面——你报出的位置才有意义。本工具在浏览器本地完成救援人员实际使用的四种格式互转，全部基于 WGS84 基准面。

十进制度（DD）把经纬度写成带符号数字，如 40.712800, -74.006000，是手机指南针 App 的显示格式，也最适合电话口述。度分秒（DMS）拆成 40°42′46.08″N 74°00′21.60″W，常见于纸质地图与老式 GPS 屏幕。UTM 把地球分为 6° 投影带，以中央经线和赤道起算米制坐标——18N E 583959 N 4507351，在地图上用直尺就能量距离。MGRS 把同一 UTM 点压缩为分带号、纬度带、100 km 方格加网格字符串：18TWL8395907351，每轴五位尾数可把位置定位到约 1 米。

数学依据

所有转换基于 WGS84 椭球（长半轴 6 378 137 米，扁率 1/298.257223563）。经纬度↔UTM 采用 USGS Professional Paper 1395 的 Krueger 级数方程；MGRS 字母编号遵循 NGA 通用网格标准（NGA.STND.0037）。同一点经 UTM 或五位 MGRS 往返转换误差约半米以内——远小于消费级手机在开阔天空下约 3–10 米的 GPS 定位误差。

如何向调度报告位置

拨打当地急救电话（美加 911、欧盟及多数国家 112、中国 120），保持通话，开口先报基准面：「我使用的是 WGS84」。对方只有电话时报十进制度，有地图时可报 UTM/MGRS。再补充最近地标、步道或河谷名称、观测时间、人数与伤情。务必说明基准面：旧地图与老式设备可能使用 NAD27、ED50 或本地基准面，同样的数字在不同基准面下可相差数百米。

Frequently asked questions常见问题

Which format should I give 911?给 911 报哪种格式？

WGS84 decimal degrees are easiest by phone and match what phone compass apps show. SAR teams with a map may prefer UTM or MGRS. State the datum first either way.WGS84 十进制度最适合电话口述，也与手机指南针显示一致；搜救队有地图时更偏好 UTM 或 MGRS。无论哪种都先报基准面。

Does GPS work with no cell signal?没有手机信号 GPS 还能用吗？

Yes — position is computed directly from satellites. Offline GPS apps and many compass apps show coordinates in airplane mode; only calls and texts require service.可以——定位直接由卫星解算。离线 GPS App 与许多指南针 App 在飞行模式下仍能显示坐标；只有通话和短信需要运营商信号。

UTM vs MGRS — what is the difference?UTM 和 MGRS 有何区别？

UTM is zone plus easting/northing in metres; MGRS wraps the same point into a zone, latitude band, 100 km square and a compact grid string that is easier to say aloud and plot on a USNG-style map.UTM 是分带加米制东/北坐标；MGRS 把同一点压缩为分带、纬度带、100 km 方格与紧凑网格字符串，更适合口述与在 USNG 式地图上标绘。

Why must I say “WGS84”?为什么一定要说「WGS84」？

The same grid numbers on NAD27, ED50 or local datums can be tens to hundreds of metres away. Naming the datum removes the ambiguity; all four outputs here are WGS84.同样的网格数字在 NAD27、ED50 或本地基准面下可能相差数十到数百米。说明基准面才能消除歧义；本页四个结果全部是 WGS84。

Are my coordinates uploaded anywhere?坐标会被上传吗？

No. Everything is computed locally from published USGS/NGA projection math, and the page works offline once cached.不会。全部计算在本地依据公开的 USGS/NGA 投影数学完成；页面缓存后可离线使用。