# 温度换算

> 用 °F = °C × 9/5 + 32 换算摄氏度与华氏度，并将两者换算为开尔文。支持兰氏度和列氏度；拒绝低于绝对零度的值。

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

Temperature scales differ in the size of a degree and in where zero sits, so a conversion adds an offset as well as multiplying: °F = °C × 9/5 + 32, and K = °C + 273.15. The converter works through kelvin, whose zero is absolute zero, and rejects any value below it (−273.15 °C or −459.67 °F).

The default converts normal body temperature: 37 × 9/5 + 32 = 98.6 °F. Weather forecasts, oven settings and fever readings are the everyday uses; the 38 °C fever threshold is 100.4 °F.

A temperature difference converts without the offset: a rise of 10 °C is a rise of 18 °F. Rankine is the absolute scale with Fahrenheit-sized degrees, and Réaumur is a historical scale with 80 degrees between the freezing and boiling points of water.

## 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：kelvin (K), degree Celsius (°C), degree Fahrenheit (°F), degree Rankine (°R), degree Réaumur (°Ré))
- **到** (选项：kelvin (K), degree Celsius (°C), degree Fahrenheit (°F), degree Rankine (°R), degree Réaumur (°Ré))

## 结果

- 转换后的数值 — 主要结果
- 换算
- 换算系数
- 精确性

## 公式

$$
\begin{gathered} t_{\text{°F}} = t_{\text{°C}} \times \tfrac{9}{5} + 32 \\ T_{\text{K}} = t_{\text{°C}} + 273.15 \\ T_{\text{°R}} = T_{\text{K}} \times \tfrac{9}{5} \\ t_{\text{°Ré}} = t_{\text{°C}} \times \tfrac{4}{5} \end{gathered}
$$

## 计算示例

### Body temperature, 37 °C in °F

- 数值: 37 °C
- 从: degree Celsius (°C)
- 到: degree Fahrenheit (°F)
- **转换后的数值: 98.6 °F**
- **换算: 37 °C = 98.6 °F**
- **精确性: 精确**
- 核验来源：°F = °C × 9/5 + 32 (NIST SP 811 §4.2.1.1): 37 × 1.8 + 32 = 98.6

### −40 is the same in both scales

- 数值: -40 °C
- 从: degree Celsius (°C)
- 到: degree Fahrenheit (°F)
- **转换后的数值: -40 °F**
- 核验来源：−40 × 9/5 + 32 = −40

### Absolute zero in °F

- 数值: 0 K
- 从: kelvin (K)
- 到: degree Fahrenheit (°F)
- **转换后的数值: -459.67 °F**
- **精确性: 精确**
- 核验来源：0 K = −273.15 °C; −273.15 × 9/5 + 32 = −459.67 °F (NIST SP 811 App. B.9)

### 100 °F in °C

- 数值: 100 °F
- 从: degree Fahrenheit (°F)
- 到: degree Celsius (°C)
- **转换后的数值: 37.7777777778 °C**
- **精确性: 定义精确，结果为循环小数**
- 核验来源：(100 − 32) × 5/9 = 340/9 (Python 3.8 fractions from the legal definitions)

### 300 K in °R

- 数值: 300 K
- 从: kelvin (K)
- 到: degree Rankine (°R)
- **转换后的数值: 540 °R**
- **换算系数: 1.8**
- 核验来源：°R = K × 9/5 (NIST SP 811 App. B.9)

## 常见问题

### How do I convert Celsius to Fahrenheit?

Multiply by 9/5 (1.8) and add 32. For 37 °C, 37 × 1.8 = 66.6, and adding 32 gives 98.6 °F. To go back, subtract 32 and multiply by 5/9: (100 °F − 32) × 5/9 = 37.78 °C. NIST SP 811 states the same relation as t/°F = 1.8 t/°C + 32.

### Is 98.6 °F normal body temperature?

98.6 °F is the exact Fahrenheit value of 37 °C, the average Carl Wunderlich published in 1868; individual readings vary with the person, the time of day and where the thermometer goes. For illness the threshold matters more: the NHS treats 38 °C or above as a high temperature, and the US CDC defines fever as 100.4 °F, the same value.

### At what temperature are Celsius and Fahrenheit equal?

At −40. Setting the two numbers equal in °F = °C × 9/5 + 32 gives x = 1.8x + 32, so x = −40, and −40 °C is exactly −40 °F. It is the only crossing point because the degrees differ in size; above −40 the Fahrenheit number is always the larger one.

### How do I convert Celsius to kelvin?

Add 273.15: 25 °C is 298.15 K, and absolute zero, 0 K, is −273.15 °C. A kelvin is the same size as a Celsius degree and, since 2019, is defined by fixing the Boltzmann constant at 1.380649 × 10⁻²³ J/K (BIPM SI Brochure). Kelvin is written without a degree sign.

### Why is a 10 °C rise an 18 °F rise and not 50 °F?

Because a difference has no zero point to shift. One Celsius degree is 1.8 Fahrenheit degrees, so a change of 10 °C is a change of 18 °F; the +32 applies only to a reading on the scale. The converter's steps show the offset and the per-degree factor separately for this reason.

### “温度换算”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：5。 例如，“Body temperature, 37 °C in °F”根据°F = °C × 9/5 + 32 (NIST SP 811 §4.2.1.1): 37 × 1.8 + 32 = 98.6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; BIPM SI Brochure, 9th edition (2019), §2.3.1 — the kelvin and degree Celsius.

## 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)
- [BIPM SI Brochure, 9th edition (2019), §2.3.1 — the kelvin and degree Celsius](https://www.bipm.org/en/publications/si-brochure)