# 速度換算ツール

> 正確な係数で mph から km/h、km/h から mph、m/s、ノットへ換算します。ft/s、海面高度のマッハ数、光速にも対応します。

操作できるページ：https://www.calcopenly.com/ja/conversion/speed-converter
分野：単位換算ツール

Each speed unit is a fixed number of metres per second. The road and sea units are exact: a mile per hour is 0.44704 m/s because the mile is 1,609.344 m, a kilometre per hour is 1/3.6 m/s, and a knot, one nautical mile per hour, is 1,852/3,600 m/s.

The default converts 60 mph to 96.56064 km/h, the figure a UK or US driver needs on metric roads. Sailors and pilots work in knots, and 1 knot is exactly 1.852 km/h.

Mach is fixed here at 340.294 m/s, the speed of sound in the International Standard Atmosphere at sea level and 15 °C, and results that use it are marked approximate because the real speed of sound falls with temperature. The speed of light is exactly 299,792,458 m/s by definition.

## 入力

- **値**: 変換元の単位で数値を入力するか、単位付きの数値を入力します
- **変換元** (選択肢：metre per second (m/s), kilometre per hour (km/h), mile per hour (mph), knot (kn), foot per second (ft/s), kilometre per second (km/s), Mach (sea level) (Ma), speed of light (c))
- **変換先** (選択肢：metre per second (m/s), kilometre per hour (km/h), mile per hour (mph), knot (kn), foot per second (ft/s), kilometre per second (km/s), Mach (sea level) (Ma), speed of light (c))

## 結果

- 変換後の値 — 主な結果
- 単位換算
- 換算係数
- 正確さ

## 計算式

$$
\begin{gathered} x_{\text{to}} = x_{\text{from}} \times \dfrac{f_{\text{from}}}{f_{\text{to}}} \\ f = \text{one unit expressed in } \text{m/s} \end{gathered}
$$

## 計算例

### 60 mph in km/h

- 値: 60 mph
- 変換元: mile per hour (mph)
- 変換先: kilometre per hour (km/h)
- **変換後の値: 96.56064 km/h**
- **正確さ: 正確**
- 照合元：60 × 1609.344 m / 1000 = 96.56064 km/h (1 mi = 1609.344 m, NIST HB 44)

### 1 knot in km/h

- 値: 1 kn
- 変換元: knot (kn)
- 変換先: kilometre per hour (km/h)
- **変換後の値: 1.852 km/h**
- 照合元：1 knot = 1 nautical mile per hour = 1852 m/h (NIST SP 811 App. B)

### 100 km/h in m/s

- 値: 100 km/h
- 変換元: kilometre per hour (km/h)
- 変換先: metre per second (m/s)
- **変換後の値: 27.7777777778 m/s**
- **正確さ: 定義は正確、結果は循環小数**
- 照合元：100000 m / 3600 s = 250/9 (Python 3.8 fractions from the legal definitions)

### Speed of light in km/s

- 値: 1 c
- 変換元: speed of light (c)
- 変換先: kilometre per second (km/s)
- **変換後の値: 299,792.458 km/s**
- 照合元：c = 299,792,458 m/s exactly (SI definition of the metre)

### Mach 1 at sea level (approximate)

- 値: 1 Ma
- 変換元: Mach (sea level) (Ma)
- 変換先: kilometre per hour (km/h)
- **変換後の値: 1,225.0584 km/h**
- **正確さ: 近似**
- 照合元：340.294 m/s (ISA sea level, 15 °C) × 3.6 = 1225.0584 km/h

## よくある質問

### How do I convert mph to km/h?

Multiply by 1.609344: 60 mph × 1.609344 = 96.56064 km/h, and 70 mph is 112.65 km/h. The factor is exact because a mile is exactly 1,609.344 m. Multiplying by 1.6 is a mental shortcut that comes out 0.6% low; to go from km/h to mph, multiply by 0.621371.

### How do I convert km/h to m/s?

Divide by 3.6, because an hour has 3,600 seconds and a kilometre 1,000 metres. 100 km/h is 27.78 m/s and 36 km/h is exactly 10 m/s. Multiply by 3.6 to go back: a sprinter at 10 m/s is running 36 km/h, or 22.37 mph.

### What is a knot in mph and km/h?

One knot is exactly 1.852 km/h, about 1.15078 mph or 0.514444 m/s. It is one nautical mile (1,852 m) per hour, the speed unit of shipping and aviation, so a 30-knot wind is 55.56 km/h or 34.52 mph.

### How fast is Mach 1?

In the International Standard Atmosphere at sea level (15 °C) it is 340.294 m/s, which is 1,225.06 km/h or 761.22 mph, the value this converter uses. The speed of sound depends on air temperature, so at 11 km altitude, where the standard atmosphere is −56.5 °C, Mach 1 is about 295 m/s or 1,062 km/h.

### Why is the speed of light an exact number?

Because the metre is defined from it. Since 1983 the metre has been the distance light travels in vacuum in 1/299,792,458 of a second, which fixes c at exactly 299,792,458 m/s, or 1,079,252,848.8 km/h. Converting c into any unit here is therefore exact.

### 「速度換算ツール」の精度はどのくらいですか？

精度は入力値と計算方法の前提に依存します。十進演算には有効数字50桁を使いますが、推定、数値計算手法、元データの精度はそれより低い場合があります。表示の丸め処理でこれらの制約がなくなるわけではありません。 独立した出典の解答と照合した計算例：5。 例えば、「60 mph in km/h」は60 × 1609.344 m / 1000 = 96.56064 km/h (1 mi = 1609.344 m, NIST HB 44)と照合しています。

### この計算方法の出典は何ですか？

NIST SP 811 (2008), Guide for the Use of the SI, Appendix B — conversion factors; NIST Handbook 44, Appendix C — General tables of units of measurement.

## 出典

- [NIST SP 811 (2008), Guide for the Use of the SI, Appendix B — conversion factors](https://www.nist.gov/pml/special-publication-811)
- [NIST Handbook 44, Appendix C — General tables of units of measurement](https://www.nist.gov/pml/owm/nist-handbook-44-current-edition)