座標形式変換ツール（度分秒／度分／小数度）
ガイド
Coordinate Format Converter
Convert geographic coordinates between the three common formats — Decimal Degrees (DD), Degrees Decimal Minutes (DDM), and Degrees Minutes Seconds (DMS) — with full precision and no rounding surprises. Paste a latitude and longitude in any format and instantly get all three representations side by side, complete with a live OpenStreetMap preview pin.
The tool also supports batch mode for converting many coordinate pairs in one go, with CSV download. Conversion runs entirely in your browser, so nothing is sent to a server.
使用方法
- ピック Single Coordinate mode (default) or Batch mode.
- Type or paste a latitude in any format:
51.5074,51 30.444 N、 または51° 30' 26.64" N. - Do the same for longitude. The tool auto-detects the format you used.
- Read off the converted values in DD, DDM and DMS, each with its own copy button.
- 調整 小数点精度 to control how many decimal places are kept. The map updates as you type.
- For batch mode, paste one coordinate pair per line (comma- or space-separated) and download the combined CSV.
機能
- Three formats at once – Decimal Degrees, Degrees Decimal Minutes, and Degrees Minutes Seconds are produced from a single input.
- Format auto-detection – the parser figures out whether you entered DD, DDM or DMS based on the number of tokens you provided.
- Hemisphere handling – supports both N/S/E/W letters and signed decimal notation, with proper conversion between the two.
- バッチ変換 – convert hundreds of coordinate pairs at once and download the result as CSV.
- Map preview – pinned coordinates appear on an interactive OpenStreetMap so you can sanity-check the result visually.
- 設定可能な精度 – choose from 2 to 8 decimal places (roughly 1.1 km down to 1.1 mm).
- クライアントサイドのみ – everything runs in your browser, no coordinates leave your device.
- Copy individual fields – each output (latitude, longitude, or full pair) has a dedicated copy button.
Why Format Matters
A coordinate written as 51.5074 looks innocent, but a single dropped decimal places you in a different neighbourhood. The Earth’s circumference is roughly 40,000 km, so one degree of latitude is about 111 km. That means the fourth decimal place is worth about 11 m, the fifth is about 1.1 m, and the sixth is about 11 cm. Tools like GPS receivers, surveying equipment, and aviation systems each have a preferred format, so converting cleanly between them — without truncating precision — is critical when feeding data between systems.
よくある質問
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What is the difference between DD, DDM and DMS?
Decimal Degrees (DD) expresses a coordinate as a single signed decimal number, like 51.5074. Degrees Decimal Minutes (DDM) splits it into integer degrees plus a fractional minutes value, like 51° 30.444' N. Degrees Minutes Seconds (DMS) splits it further into integer degrees, integer minutes, and a fractional seconds value, like 51° 30' 26.64" N. All three represent the same physical point on Earth; they differ only in notation.
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Why are signed decimals used instead of N/S and E/W letters?
Signed decimals encode the hemisphere in the sign of the number: positive latitude is north, negative is south; positive longitude is east, negative is west. This is more compact and easier for software to process arithmetically, since you do not need to parse a letter separately. The letter notation (N, S, E, W) is more common in human-facing contexts like nautical charts and aviation.
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How precise are these formats in practice?
Latitude precision is roughly 111 km per degree at any point on Earth. So 1 decimal degree is about 11.1 km, 0.001 is about 111 m, 0.00001 is about 1.1 m, and 0.0000001 is about 11 cm. For DMS, one second of latitude is about 31 m, and one tenth of a second is about 3 m. Longitude precision shrinks toward the poles because meridians converge, so a longitude second at the equator is about 31 m but only about 22 m at 45° latitude.
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What is WGS84 and does it matter here?
WGS84 (World Geodetic System 1984) is the reference ellipsoid that GPS and most modern mapping uses to define what latitude and longitude mean physically. This converter assumes WGS84 throughout, which is what almost every consumer GPS device, web map, and smartphone reports. If you are working with older datums like NAD27 or local national grids, you would need a separate datum transformation step before or after format conversion.
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Why do my converted seconds sometimes round to a slightly different value?
Decimal to DMS conversion involves splitting a decimal number into three integer or near-integer parts, and floating point arithmetic can introduce tiny rounding errors at the boundaries. For example, a coordinate that should give exactly 30 seconds might compute as 29.9999999, which would display as 30 only after rounding. This converter rounds the seconds field cleanly and carries any overflow up into minutes and degrees so you never see 60'00" or similar invalid values.
