# 油耗换算器（mpg 转 L/100 km）

> 在 mpg、L/100 km 和 km/L 之间换算，支持美制和英制加仑：L/100 km = 235.215 ÷ US mpg 或 282.481 ÷ UK mpg。

交互版本：https://www.calcopenly.com/zh/conversion/fuel-economy-converter
主题：单位换算器

Fuel economy comes in two shapes. Miles per gallon and kilometres per litre measure distance per unit of fuel; litres per 100 km measures fuel per distance. The two are reciprocals, so L/100 km = 100 ÷ (km/L), and a US mpg figure converts as L/100 km = 235.215 ÷ mpg.

The default converts 30 US mpg to 7.84 L/100 km. Comparing cars across markets is the usual reason: the US quotes mpg with a 3.785 L gallon, the UK quotes mpg with a 4.546 L gallon while selling fuel by the litre, most of Europe uses L/100 km and India uses km/L.

Because the scales are reciprocal, equal steps in mpg are not equal fuel savings: going from 10 to 20 mpg saves 5 gallons per 100 miles, while going from 30 to 50 mpg saves 1.33. The chart plots that curve.

## 输入

- **数值**: 输入源单位下的数值，也可以输入带有自身单位的数值
- **从** (选项：kilometre per litre (km/L), litre per 100 km (L/100 km), mile per US gallon (mpg (US)), mile per imperial gallon (mpg (UK)))
- **到** (选项：kilometre per litre (km/L), litre per 100 km (L/100 km), mile per US gallon (mpg (US)), mile per imperial gallon (mpg (UK)))

## 结果

- 转换后的数值 — 主要结果
- 换算
- 换算系数
- 精确性

## 公式

$$
\begin{gathered} \text{L/100 km} = \dfrac{100}{\text{km/L}} \\ \text{km/L} = \text{mpg}_{\text{US}} \times \dfrac{1.609344}{3.785411784} = \text{mpg}_{\text{UK}} \times \dfrac{1.609344}{4.54609} \\ \text{L/100 km} \approx \dfrac{235.215}{\text{mpg}_{\text{US}}} \approx \dfrac{282.481}{\text{mpg}_{\text{UK}}} \end{gathered}
$$

## 计算示例

### 30 mpg (US) in L/100 km

- 数值: 30 mpg (US)
- 从: mile per US gallon (mpg (US))
- 到: litre per 100 km (L/100 km)
- **转换后的数值: 7.8404861111 L/100 km**
- **精确性: 定义精确，结果为循环小数**
- 核验来源：100 ÷ (30 × 1.609344 km / 3.785411784 L) = 112903/14400 (Python 3.8 fractions from the legal definitions)

### 10 L/100 km in mpg (US)

- 数值: 10 L/100 km
- 从: litre per 100 km (L/100 km)
- 到: mile per US gallon (mpg (US))
- **转换后的数值: 23.5214583333 mpg (US)**
- 核验来源：(100 / 10) km/L ÷ (1.609344/3.785411784) = 112903/4800 (Python 3.8 fractions from the legal definitions)

### 40 mpg (UK) in mpg (US)

- 数值: 40 mpg (UK)
- 从: mile per imperial gallon (mpg (UK))
- 到: mile per US gallon (mpg (US))
- **转换后的数值: 33.3069673852 mpg (US)**
- 核验来源：40 × 3.785411784 / 4.54609 (Python 3.8 fractions from the legal definitions)

### Crossover: 10 km/L equals 10 L/100 km

- 数值: 10 km/L
- 从: kilometre per litre (km/L)
- 到: litre per 100 km (L/100 km)
- **转换后的数值: 10 L/100 km**
- **精确性: 精确**
- 核验来源：100 / 10 = 10 — the one value where km/L and L/100 km coincide

## 常见问题

### How do I convert mpg to L/100 km?

Divide 235.215 by a US mpg figure, or 282.481 by a UK mpg figure. 30 US mpg is 7.84 L/100 km and 50 UK mpg is 5.65 L/100 km. The constants are 100 × 3.785411784 ÷ 1.609344 and 100 × 4.54609 ÷ 1.609344, built from the exact gallon and mile.

### Why is UK mpg higher than US mpg for the same car?

Because the imperial gallon is 20% larger: 4.54609 L against 3.785411784 L. A car doing 40 mpg on UK figures does 33.3 mpg in US gallons, and 40 US mpg is 48.0 UK mpg. Both describe the same fuel use; 40 UK mpg is 7.06 L/100 km.

### Why does going from 10 to 20 mpg save more fuel than 30 to 50 mpg?

Because fuel used is distance divided by mpg. Over 100 miles, 10 mpg burns 10 gallons and 20 mpg burns 5, a saving of 5; 30 mpg burns 3.33 and 50 mpg burns 2, a saving of 1.33. Larrick and Soll called this the “MPG illusion” (Science, 2008); L/100 km avoids it because it measures fuel directly.

### How do I convert km/L to L/100 km?

Divide 100 by the km/L figure: 20 km/L is 5 L/100 km and 12.5 km/L is 8 L/100 km. At 10 km/L the two numbers are equal. To go from km/L to US mpg, multiply by 2.35215, so 15 km/L is 35.3 US mpg.

### Is a lower L/100 km better?

Yes. L/100 km counts fuel used, so a smaller number means less fuel: 5 L/100 km is twice as economical as 10 L/100 km. With mpg and km/L a larger number is better. The product of the two stays fixed, 235.215 for L/100 km and US mpg, which is why one falls as the other rises.

### “油耗换算器（mpg 转 L/100 km）”有多准确？

准确性取决于输入值和方法的假设。十进制运算使用50位有效数字，但估算、数值方法和源数据的精度可能较低；显示时的舍入并不能消除这些限制。 已按独立来源核验的计算示例：4。 例如，“30 mpg (US) in L/100 km”根据100 ÷ (30 × 1.609344 km / 3.785411784 L) = 112903/14400 (Python 3.8 fractions from the legal definitions)进行核验。

### 这种方法出自哪里？

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.

## 来源

- [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)