How do I convert Celsius to Fahrenheit?

Multiply the Celsius value by 9/5 and add 32. So 20 °C becomes 20 × 9/5 + 32 = 68 °F. To go the other way, subtract 32 first then multiply by 5/9.

How do I convert Celsius to Kelvin?

Add 273.15 to the Celsius value. 25 °C is 298.15 K. Kelvin uses the same degree size as Celsius, so the gap between two temperatures is identical in both scales — only the zero point differs.

What is the Rankine scale and how does it relate to Fahrenheit?

Rankine is an absolute scale that starts at absolute zero but uses Fahrenheit-sized degrees. Convert from Fahrenheit by adding 459.67, so 32 °F equals 491.67 °R. It is mostly used in some US engineering and thermodynamics work.

At what temperature are Celsius and Fahrenheit equal?

They read the same at −40, where −40 °C equals −40 °F. This is the single crossover point of the two scales and a handy sanity check for any converter.

What is absolute zero on each scale?

Absolute zero is 0 K, which equals −273.15 °C, −459.67 °F and 0 °R. Nothing can be colder, so the tool flags any value that would fall below it as physically impossible.

Is my data sent anywhere?

No. Every conversion is pure arithmetic performed in your browser using built-in JavaScript. No values are uploaded, logged or stored on a server.

What is the Temperature Converter?

Free temperature converter for Celsius, Fahrenheit, Kelvin and Rankine. Type into any field and all the others update live, with a swap button and a full reference table. Runs entirely in your browser. It runs free in your browser on Gera Tools, with nothing uploaded.

Temperature Converter

Name: Temperature Converter
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

A temperature converter that handles all four common scales — Celsius (°C), Fahrenheit (°F), Kelvin (K) and Rankine (°R) — using the exact defining formulas rather than rounded approximations. It is built for cooks, students, scientists and engineers who need a quick, trustworthy conversion without reaching for a phone app or a server round-trip. Type a value into the focused from/to box, or straight into any of the four scale cards, and every other field updates instantly.

The three scales and their exact formulas

The tool converts everything through Kelvin as a single canonical baseline, then fans the result back out to each scale. Working through one absolute scale keeps the maths consistent and avoids the rounding errors you get when chaining conversions one step at a time. Whichever field you last edited becomes the anchor: its raw text is preserved exactly while the other three are recomputed.

The conversions are governed by these relationships. Celsius and Kelvin share a degree size and differ only by the offset 273.15. Fahrenheit and Rankine share a degree size — each one is 5/9 of a Celsius degree. Fahrenheit and Rankine differ by the offset 459.67. Because the tool stores the canonical value as a single Kelvin number, the swap button can flip the from and to scales while preserving the exact physical temperature. The converter also knows that absolute zero is 0 K, so any entry that would compute below it is flagged as physically impossible — useful for catching a mistyped sign or a stray minus.

Worked example

Suppose you have a recipe written in Fahrenheit and your oven dial is in Celsius. Enter 350 and set the from scale to Fahrenheit. The tool computes the Kelvin baseline as (350 + 459.67) × 5/9 = 449.817 K, then reports 176.667 °C — round that to about 177 °C (a moderate oven). Switch the to scale to Kelvin and you read 449.82 K; to Rankine and you read 809.67 °R. A quicker everyday check: −40 °C and −40 °F are the same temperature, the one point where the two everyday scales meet.

Conversion reference

From → To	Formula
Celsius → Fahrenheit	F = C × 9/5 + 32
Fahrenheit → Celsius	C = (F − 32) × 5/9
Celsius → Kelvin	K = C + 273.15
Kelvin → Celsius	C = K − 273.15
Celsius → Rankine	R = (C + 273.15) × 9/5
Fahrenheit → Rankine	R = F + 459.67
Kelvin → Rankine	R = K × 9/5
Rankine → Kelvin	K = R × 5/9

A few anchor points to sanity-check any conversion: water freezes at 0 °C / 32 °F / 273.15 K / 491.67 °R, water boils at 100 °C / 212 °F / 373.15 K / 671.67 °R, and absolute zero sits at 0 K / −273.15 °C / −459.67 °F / 0 °R.

Every figure is calculated in your browser — no numbers are uploaded or stored.

Where the scales come from — and why Kelvin is different

Fahrenheit and Celsius are interval scales anchored to arbitrary reference points (originally brine and body temperature for Fahrenheit; water’s freezing and boiling for Celsius). Kelvin is an absolute scale: zero kelvin is absolute zero, the point of minimum thermal energy, which is why Kelvin has no negative values and no degree symbol. Since the 2019 redefinition of SI units, the kelvin is defined by fixing the Boltzmann constant — the definition maintained by the BIPM in the SI Brochure — rather than by any property of water. For unit style and conversion factors, NIST Special Publication 811 is the standard reference.

Three anchor facts make mental conversion easy:

−40 is the crossover: −40 °C = −40 °F exactly, the only point where the two scales agree.
A Celsius degree is 1.8 Fahrenheit degrees: intervals scale by 9/5 even though the zero points differ.
0 K = −273.15 °C exactly: the Celsius and Kelvin scales are offset by a defined constant, so converting between them is pure addition.

Quick sanity checks for converted values

When a conversion feels off, test it against remembered anchors: room temperature ≈ 20 °C / 68 °F / 293 K; body temperature ≈ 37 °C / 98.6 °F; water boils at 100 °C / 212 °F at sea level (and lower at altitude — about 1 °C less per 300 m, which is a pressure effect no unit conversion captures). A converted value that violates one of these anchors means an input slip — typically entering a Fahrenheit reading in the Celsius field.