Temperature Converter

What the Temperature Converter Does

Three linked fields show the same temperature on the three common scales. Edit whichever one you know — say 25 in Celsius — and Fahrenheit (77) and Kelvin (298.15) fill in at once. Change the Fahrenheit box instead and Celsius and Kelvin follow.

The result is rounded to two decimal places, which is fine for weather, cooking and most science homework. There is no conversion table or lookup involved; each scale is computed directly from the one you typed.

How It Works

Temperature is not a ratio, so you cannot convert it with a single multiplier the way you convert metres to feet. Each scale has a different zero point, so the conversion is linear with an offset — a multiply and an add. Celsius to Fahrenheit multiplies by 9/5 and adds 32; Celsius to Kelvin just adds 273.15, because the degree is the same size in both.

Whichever box you edit becomes the source. The tool works out the others from it directly — for example Fahrenheit to Celsius subtracts 32 then multiplies by 5/9 — so there is no accumulated rounding from hopping scale to scale.

Data source & conversion logic

The conversions use the defined relationships between the scales: the freezing and boiling points of water anchor Celsius and Fahrenheit, and the Kelvin scale starts at absolute zero, −273.15 °C. Since the 2019 SI revision the kelvin is defined through the Boltzmann constant, but for everyday conversion the fixed 273.15 offset is all that matters.

1. Read the edited field. Whichever box you type in — Celsius, Fahrenheit or Kelvin — becomes the source value.
2. Convert to the others directly. Apply the exact pairwise formula to each of the other two scales, computed from the source rather than chained through a third.
3. Apply the offset. Add or subtract the scale's zero-point offset (32 for Fahrenheit, 273.15 for Kelvin) alongside the 9/5 or 5/9 factor.
4. Round and show. Round each result to two decimal places and display all three together.

Temperature conversion formulas

Celsius and Fahrenheit read the same at −40°. Results are rounded to two decimals.

Technical Details

Standards & references

• Celsius scale — 0 °C and 100 °C sit at the freezing and boiling points of water at standard pressure; the degree is one hundredth of that interval.
• Fahrenheit scale — 32 °F freezing and 212 °F boiling — a 180-degree interval, so each Fahrenheit degree is 5/9 of a Celsius degree.
• Kelvin (SI) — starts at absolute zero (−273.15 °C); since 2019 the kelvin is fixed through the Boltzmann constant, 1.380649×10⁻²³ J/K. Its degree is the same size as Celsius.

Accuracy & Limitations

Rounded to two decimal places. That is more than enough for weather, cooking, medicine and school science; high-precision metrology would keep more digits.

It does not stop you entering a temperature below absolute zero. Type −300 °C and it will convert the number, even though nothing can be that cold — the tool does the arithmetic, it does not police physics.

Only Celsius, Fahrenheit and Kelvin are offered. Rankine (absolute Fahrenheit) and the historical Réaumur scale are not included.

The formulas are exact, not approximations — the only loss is the final two-decimal rounding. A value like 100 °F gives 37.78 °C, the correctly rounded figure.

Real-World Use Cases

When to use it — and when not to

Need Rankine, or to convert non-temperature units? This tool is Celsius, Fahrenheit and Kelvin only — use the unit converter for length, weight and volume.

Frequently Asked Questions

References

• Conversion of scales of temperature (Wikipedia)
• Kelvin (Wikipedia)
• Celsius to Fahrenheit (Metric Conversions)

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