Temperature Converter

How the Temperature Converter Works

A temperature converter changes a reading from one scale to another using fixed mathematical relationships. The three scales you will meet most often are Celsius (°C), Fahrenheit (°F) and Kelvin (K). Celsius is used by most of the world for everyday weather, Fahrenheit is standard in the United States, and Kelvin is the SI unit used in science and engineering.

Unlike length or mass, temperature scales do not share a common zero point, so converting between them requires both a scaling factor and an offset. Celsius and Kelvin share the same degree size but start at different zero points, while Fahrenheit uses a smaller degree and a different zero. Once you know the formulas, every conversion becomes simple arithmetic.

Temperature Conversion Formulas

Use these exact formulas for accurate results every time:

• Celsius to Fahrenheit: F = C × 9/5 + 32
• Fahrenheit to Celsius: C = (F − 32) × 5/9
• Celsius to Kelvin: K = C + 273.15
• Kelvin to Celsius: C = K − 273.15
• Fahrenheit to Kelvin: K = (F − 32) × 5/9 + 273.15
• Kelvin to Fahrenheit: F = (K − 273.15) × 9/5 + 32

For example, to convert 25 °C to Fahrenheit: 25 × 9/5 + 32 = 45 + 32 = 77 °F. To convert that same 25 °C to Kelvin: 25 + 273.15 = 298.15 K. The factor 9/5 (or 1.8) reflects that one Celsius degree spans 1.8 Fahrenheit degrees.

Common Temperature Conversions

The table below shows reference points you will use most often, including the freezing and boiling points of water and normal body temperature.

Celsius (°C)	Fahrenheit (°F)	Kelvin (K)
-40	-40	233.15
0	32	273.15
20	68	293.15
37	98.6	310.15
100	212	373.15

Notice that −40 is the single point where Celsius and Fahrenheit read exactly the same value. Water freezes at 0 °C (32 °F) and boils at 100 °C (212 °F) at sea level, while average human body temperature is about 37 °C (98.6 °F).

Why Kelvin Matters in Science

Kelvin is an absolute scale, meaning its zero (0 K, or −273.15 °C) is absolute zero, the lowest possible temperature where molecular motion theoretically stops. Because Kelvin never goes negative, it is essential for thermodynamics, gas laws and physics calculations where ratios of temperature matter.

A key point: Kelvin values are written without a degree symbol, so you say "298 kelvin," not "298 degrees Kelvin." Since a one-degree change in Celsius equals a one-kelvin change, you only need to add or subtract 273.15 to move between them, with no scaling factor required. This makes Kelvin and Celsius the easiest pair to convert.

Tips for Accurate Temperature Conversions

Getting temperature conversions right comes down to applying the offset and the scaling factor in the correct order. A common mistake when converting Fahrenheit to Celsius is to multiply before subtracting. Always subtract 32 first, then multiply by 5/9, because the 32-degree offset accounts for the difference in where the two scales place the freezing point of water.

When working with Kelvin, remember there is no scaling involved with Celsius at all, only the 273.15 offset. Rounding too early can introduce small errors, so keep the full decimal until your final step, especially in scientific work where 273.15 (not 273) is the precise constant. For quick mental estimates, you can approximate Celsius to Fahrenheit by doubling the Celsius value and adding 30, though this is only a rough guide.

It also helps to sanity-check your answer against a known reference point. If you convert a hot summer day of 35 °C and get 95 °F, that matches the expectation that 35 °C is a warm temperature. If a result looks impossibly high or low, you likely applied a formula in the wrong direction. Our converter handles all of this automatically, but understanding the math lets you verify any reading with confidence, whether for cooking, weather, travel or laboratory use.