How do I convert Celsius to Fahrenheit?

To convert Celsius to Fahrenheit, multiply the Celsius temperature by 9/5 (or 1.8), then add 32. The formula is: F = (C × 9/5) + 32. For example, 25°C = (25 × 1.8) + 32 = 77°F.

What is absolute zero in different temperature scales?

Absolute zero, the coldest possible temperature, is 0 Kelvin, -273.15°C, or -459.67°F. At this temperature, all molecular motion stops.

Why does the US use Fahrenheit instead of Celsius?

The US adopted the Fahrenheit scale before the metric system became widespread. While most countries switched to Celsius, the US retained Fahrenheit for everyday use due to historical precedent and the cost of conversion.

What is Kelvin used for?

Kelvin is the SI unit for temperature used in scientific work. It starts at absolute zero (0 K), making it ideal for physics, chemistry, and engineering calculations where negative temperatures would be problematic.

Temperature Converter Online 2026 | Celsius, Fahrenheit, Kelvin

Q: At what temperature are Celsius and Fahrenheit equal?

Celsius and Fahrenheit are equal at -40 degrees. At this temperature, -40°C = -40°F. This is the only point where both scales intersect.

What is a Temperature Converter?

A temperature converter transforms temperature measurements from one scale to another. Unlike other unit conversions that use simple multiplication, temperature conversion requires formulas because the scales have different zero points and interval sizes.

This converter supports the three most common temperature scales: Celsius (used worldwide), Fahrenheit (used in the US), and Kelvin (used in science), plus Rankine for specialized applications.

How Does Temperature Conversion Work?

Temperature conversion is different from other unit conversions because:

Different zero points: 0°C is the freezing point of water, while 0°F is an arbitrary point based on a salt/ice mixture.
Different interval sizes: A 1-degree change in Celsius equals a 1.8-degree change in Fahrenheit.
Requires formulas: Simple multiplication won't work; you must use conversion formulas.

Temperature Conversion Formulas

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

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

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

Rankine:
°R = °F + 459.67
°R = K × 9/5

Key Temperature Reference Points

Absolute Zero: 0 K = -273.15°C = -459.67°F (coldest possible temperature)
Water Freezes: 273.15 K = 0°C = 32°F
Water Boils: 373.15 K = 100°C = 212°F (at sea level)
Human Body: 310.15 K = 37°C = 98.6°F (normal temperature)
Room Temperature: ~295 K = ~22°C = ~72°F
C = F: -40°C = -40°F (only point where both scales equal)

Benefits of Using This Converter

Instant results: See conversions update in real-time as you type.
All major scales: Supports Celsius, Fahrenheit, Kelvin, and Rankine.
High precision: Accurate calculations using exact formulas.
Educational: Learn how temperature scales relate to each other.
No app required: Works directly in your browser on any device.

Understanding Temperature Scales

Celsius (°C): Created by Anders Celsius in 1742. Based on water: 0° at freezing, 100° at boiling (at standard pressure). Used by most countries worldwide and in scientific contexts.

Fahrenheit (°F): Created by Daniel Fahrenheit in 1724. Originally based on three reference points including a salt/ice mixture. Used in the United States for weather, cooking, and everyday life.

Kelvin (K): The SI unit of temperature. Starts at absolute zero with the same interval size as Celsius. Essential for scientific calculations, especially thermodynamics.

Rankine (°R): An absolute scale like Kelvin but using Fahrenheit-sized degrees. Used in some engineering applications, particularly in the US.

Frequently Asked Questions

How do I quickly estimate Celsius to Fahrenheit?

For a rough estimate, double the Celsius value and add 30. Example: 20°C → (20 × 2) + 30 = 70°F (actual: 68°F). This works well for everyday temperatures.

Why is there no degree symbol for Kelvin?

Kelvin is written without a degree symbol (K, not °K) because it's an absolute scale. The "degree" in °C and °F implies a relative scale, while Kelvin measures absolute thermodynamic temperature.

What temperature are Celsius and Fahrenheit equal?

Celsius and Fahrenheit are equal at exactly -40 degrees. You can verify: (-40 × 9/5) + 32 = -72 + 32 = -40°F.

Why do scientists use Kelvin?

Kelvin is essential for thermodynamics because it starts at absolute zero. Calculations involving gas laws, energy, and entropy require absolute temperature. Negative temperatures would cause mathematical problems.

Is 0 Kelvin possible?

Absolute zero (0 K) cannot be reached according to the third law of thermodynamics. Scientists have cooled matter to billionths of a degree above absolute zero, but reaching exactly 0 K is theoretically impossible.

What's normal human body temperature?

Normal body temperature is approximately 37°C (98.6°F), though it varies by individual and time of day. A fever is typically defined as 38°C (100.4°F) or higher.