# Temperature Converter

> Convert temperature: Celsius↔Fahrenheit, Celsius↔Kelvin.

## What is the Temperature Converter?

The Temperature Converter converts between three major temperature scales: Celsius (°C), Fahrenheit (°F), and Kelvin (K). It provides two conversion tabs: °C↔°F and °C↔K.

Celsius (°C) is used by virtually every country in the world for everyday temperature measurement, including Korea. It was developed by Swedish astronomer Anders Celsius in 1742 and is based on the freezing point (0°C) and boiling point (100°C) of water at standard atmospheric pressure.

Fahrenheit (°F) is primarily used in the United States and a few Caribbean nations for weather, cooking, and body temperature. German physicist Daniel Gabriel Fahrenheit created this scale in 1724, where water freezes at 32°F and boils at 212°F.

Kelvin (K) is the SI unit of thermodynamic temperature used in science and engineering. It has the same scale increment as Celsius but starts at absolute zero (-273.15°C), the theoretical lowest possible temperature. There is no degree symbol before K.

This converter is essential for understanding international weather forecasts, following American recipes, interpreting scientific data, and adjusting thermostat settings when traveling abroad.

## How to Use

1. Select a conversion tab.
• °C ↔ °F: Convert between Celsius and Fahrenheit. Most common for weather, cooking, body temperature.
• °C ↔ K: Convert between Celsius and Kelvin. Used in science, engineering, color temperature.

2. Enter a temperature value in either field.
Type a number (negative values allowed) and the conversion appears instantly.

3. Read the converted result.

Common Conversion Examples:
• Body temperature: 36.5°C = 97.7°F | 37°C = 98.6°F (normal) | 38°C = 100.4°F (fever)
• Room temperature: 20°C = 68°F | 25°C = 77°F
• Freezing point: 0°C = 32°F = 273.15 K
• Boiling point: 100°C = 212°F = 373.15 K
• Absolute zero: -273.15°C = -459.67°F = 0 K
• Oven temperatures: 180°C = 356°F | 200°C = 392°F | 220°C = 428°F

Tip: Negative values are common for Celsius winter temperatures and always valid for conversion. Kelvin cannot be negative (0 K is absolute zero).

## Conversion Formulas

■ Celsius ↔ Fahrenheit
°F = (°C × 9/5) + 32
°C = (°F - 32) × 5/9

Example: 25°C = (25 × 9/5) + 32 = 45 + 32 = 77°F
Example: 98.6°F = (98.6 - 32) × 5/9 = 66.6 × 0.5556 = 37°C

■ Celsius ↔ Kelvin
K = °C + 273.15
°C = K - 273.15

Example: 100°C = 100 + 273.15 = 373.15 K
Example: 300 K = 300 - 273.15 = 26.85°C

■ Fahrenheit ↔ Kelvin (derived)
K = (°F - 32) × 5/9 + 273.15
°F = (K - 273.15) × 9/5 + 32

■ Where the Scales Meet
-40°C = -40°F (the only point where both scales are equal)

■ Quick Reference Table
-20°C = -4°F | -10°C = 14°F | 0°C = 32°F
10°C = 50°F | 15°C = 59°F | 20°C = 68°F
25°C = 77°F | 30°C = 86°F | 35°C = 95°F
37°C = 98.6°F | 40°C = 104°F | 100°C = 212°F

■ Color Temperature (Kelvin in lighting)
2700 K = warm white (incandescent)
4000 K = neutral white
5000 K = daylight
6500 K = cool daylight (overcast)

## Helpful Tips

■ Quick Mental Conversion Tricks
• °C to °F shortcut: Double °C and add 30. Example: 20°C → 40 + 30 = 70°F (actual: 68°F). Good for rough estimates.
• °F to °C shortcut: Subtract 30, then halve. Example: 80°F → 50 ÷ 2 = 25°C (actual: 26.7°C).
• For more accuracy: Double °C, subtract 10%, add 32. Example: 25°C → 50 - 5 + 32 = 77°F (exact).

■ Important Temperature References
• Hypothermia: below 35°C (95°F) body temperature
• Normal body temp: 36.1-37.2°C (97-99°F)
• Fever: 38°C (100.4°F) and above
• Heat stroke danger: above 40°C (104°F) ambient
• Food safety 'danger zone': 4-60°C (40-140°F)
• Water for coffee: 90-96°C (195-205°F)

■ Cooking Temperature Guide
Low oven: 150°C = 300°F
Moderate: 180°C = 350°F
Hot: 200°C = 400°F
Very hot: 230°C = 450°F
Broil: 260°C = 500°F

■ Weather Context for Travelers
• US 'hot day' (95°F) = 35°C
• US 'cold day' (20°F) = -6.7°C
• Korean summer average: 25-35°C = 77-95°F
• Korean winter average: -10 to 5°C = 14-41°F

■ Common Mistakes
• Don't forget to subtract 32 first when converting °F→°C
• Kelvin has no degree symbol — write 'K', not '°K'
• Body temperature varies by individual; 37°C is average, not exact normal for everyone

## Frequently Asked Questions

### Q. Why does the US still use Fahrenheit?

The Fahrenheit scale was the standard in English-speaking countries for centuries before the metric system was developed. While most countries switched to Celsius in the 1960s-1970s during metrication, the US government's attempt to mandate the metric system in 1975 (Metric Conversion Act) was voluntary and ultimately unsuccessful. Americans are deeply accustomed to Fahrenheit for daily life — knowing that 70°F is comfortable, 32°F is freezing, and 100°F is very hot. The cost and cultural resistance to changing weather reports, thermostats, ovens, and public awareness has kept Fahrenheit in everyday use.

### Q. What temperature is considered a fever?

A body temperature of 38°C (100.4°F) or above is generally considered a fever in adults. Normal body temperature ranges from about 36.1-37.2°C (97-99°F) and varies throughout the day, being lowest in the morning and highest in the late afternoon. A 'low-grade fever' is 37.3-38°C (99.1-100.4°F). In children, a rectal temperature of 38°C or above indicates fever. Seek medical attention for adults with temperatures above 39.4°C (103°F) or fever lasting more than 3 days.

### Q. What is absolute zero and why does Kelvin start there?

Absolute zero (0 K = -273.15°C = -459.67°F) is the theoretical lowest possible temperature where all molecular motion ceases. The Kelvin scale was designed to start at this point, making it a 'thermodynamic temperature' scale with no negative values. This is essential in physics and chemistry because many equations (like the ideal gas law PV=nRT) require an absolute temperature scale to work correctly. At 0 K, a substance would have minimum possible energy. Scientists have gotten within nanokelvins of absolute zero but can never actually reach it.

### Q. Why is -40° the same in both Celsius and Fahrenheit?

This is a mathematical consequence of the conversion formula. Setting °C = °F in the equation °F = (°C × 9/5) + 32 gives us: x = (x × 9/5) + 32, which solves to x = -40. This is the unique intersection point of the two scales. Below -40°, Fahrenheit values are actually lower than Celsius values (e.g., -50°C = -58°F). Above -40°, Fahrenheit values are higher (e.g., 0°C = 32°F). This fun fact is a useful mental anchor point for understanding the relationship between the two temperature scales.

### Q. How do I convert oven temperatures between Celsius and Fahrenheit?

Most international recipes use Celsius while American recipes use Fahrenheit. Key oven conversions: 150°C = 300°F (low), 160°C = 325°F, 180°C = 350°F (moderate/standard baking), 190°C = 375°F, 200°C = 400°F (hot), 220°C = 425°F, 230°C = 450°F (very hot). Gas mark conversions: Gas 4 = 180°C = 350°F, Gas 6 = 200°C = 400°F. Note that fan-assisted (convection) ovens typically run 20°C hotter than conventional ovens, so reduce the temperature by 20°C when using fan mode.