Why are there different temperature scales?

Celsius and Fahrenheit were developed as relative scales anchored to everyday physical benchmarks such as the freezing and boiling points of water, whereas Kelvin is an absolute thermodynamic scale starting at absolute zero (0 K) used in physics, chemistry, and engineering.

What is the zero point of Celsius, Fahrenheit, and Kelvin?

Temperature cannot be converted by simple multiplication alone because each scale has a different zero point: 0 °C is the freezing point of water (equal to 32 °F and 273.15 K), 0 °F equals -17.78 °C, and 0 K is absolute zero (-273.15 °C or -459.67 °F), the theoretical limit where all thermal motion ceases.

Temperature Converter

Convert temperatures between Celsius, Fahrenheit, and Kelvin.

Convert Temperature

Enter a value and select the units to convert between Celsius, Fahrenheit, and Kelvin.

Instant conversion

Value

From

Result

77 °F

25 °C = 77 °F

25 °C = 77 °F = 298.15 KGet Widget

You can change the units using the dropdowns above or click on a unit button.

Suggested Conversions

Common Temperature Reference Points

Here are some common temperature values in Celsius, Fahrenheit, and Kelvin. Click any preset value or arrow to load it into the converter.

Description	Celsius (°C)	Fahrenheit (°F)	Kelvin (K)
Absolute zero	-273.15	-459.67	0
Water freezing point (at 1 atm)	0	32	273.15
Comfortable room temperature	20	68	293.15
Typical warm day (25 °C benchmark)	25	77	298.15
Normal human body temperature	37	98.6	310.15
Water boiling point (at 1 atm)	100	212	373.15
Typical hot day	35	95	308.15

Temperature Conversion Formulas

Use the following formulas to convert between Celsius, Fahrenheit, and Kelvin.

Celsius to Fahrenheit

°F = (°C × 9/5) + 32

Fahrenheit to Celsius

°C = (°F − 32) × 5/9

Celsius to Kelvin

K = °C + 273.15

Example: Convert 25 °C to Fahrenheit

°F = (25 × 9/5) + 32

°F = (25 × 1.8) + 32 = 45 + 32 = 77 °F

Because Celsius, Fahrenheit, and Kelvin have different zero points (0 °C = 32 °F = 273.15 K), temperature cannot be converted by simple multiplication alone—you must apply both the scale ratio and the zero-point offset.

Convert from Celsius

Convert to Fahrenheit

Frequently Asked Questions

To convert Celsius to Fahrenheit, multiply the Celsius temperature by 9/5 (or 1.8) and then add 32: °F = (°C × 9/5) + 32. For example, to convert 25 °C: (25 × 1.8) + 32 = 45 + 32 = 77 °F.

Temperature Converter

Quick Info

Celsius (°C) is widely used worldwide for everyday temperature measurement.
Fahrenheit (°F) is commonly used in the United States.
Kelvin (K) is the SI unit of temperature and used in science and engineering.
Temperature conversion is not a simple multiplication. Each scale has a different zero point.

Temperature Scales Comparison

Celsius (°C)

Based on the freezing (0 °C) and boiling (100 °C) points of water. Widely used globally.

Fahrenheit (°F)

Commonly used in the United States. Freezing point at 32 °F and boiling point at 212 °F.

Kelvin (K)

The SI unit of temperature. Absolute scale with zero at absolute zero (-273.15 °C).

References

[1]NIST OWM · SI Units — Temperature
Source
[2]BIPM · SI Base Unit: Kelvin (K)
Source
[3]NIST SP 811 · NIST SP 811 App. B.9 (Heat & Temp)
Source

Related Categories

All Temperature Conversion Calculators (10)

Select any dedicated temperature pair below for worked examples and printable tables

Celsius to Fahrenheit (°C to °F)Fahrenheit to Celsius (°F to °C)Celsius to Kelvin (°C to K)Kelvin to Celsius (K to °C)Fahrenheit to Kelvin (°F to K)Kelvin to Fahrenheit (K to °F)Celsius to Rankine (°C to °R)Fahrenheit to Rankine (°F to °R)Rankine to Celsius (°R to °C Thermodynamic Scale)Rankine to Fahrenheit (°R to °F Absolute Scale)

Category Conversion Matrix

Simultaneous comparison of 4 units in this category

Celsius (°C)

Fahrenheit (°F)

33.8

Kelvin (K)

274.15

Rankine (°R)

493.47

Temperature Unit Definitions & Symbols

Celsius (°C)

Temperature scale where water freezes at 0 °C and boils at 100 °C.

Fahrenheit (°F)

US CUSTOMARY

Temperature scale where water freezes at 32 °F and boils at 212 °F.

Kelvin (K)

Base SI thermodynamic temperature scale starting at absolute zero (0 K = -273.15 °C).

Rankine (°R)

IMPERIAL

Absolute thermodynamic temperature scale with Fahrenheit-sized degrees (0 °R = -459.67 °F).

References

NIST · BIPM · ISO

[1]
NIST OWM (SI Units — Temperature)·Temperature Metrology Standards — Celsius (°C), Fahrenheit (°F) & Kelvin (K)
NIST OWM Standard
[2]
BIPM (SI Base Unit: Kelvin (K))·International Reference Specification for Temperature Scales
BIPM Reference
[3]
NIST SP 811 (NIST SP 811 App. B.9 (Heat & Temp))·Official Temperature Conversion Factors & Rounding Rules
NIST SP 811 Tables

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