Temperature Converter

Why There Are So Many Temperature Scales

It seems unnecessarily complicated — water boils at 100°C, 212°F, and 373.15 K, all at the same time. Three numbers for the same physical fact. The reason is historical: temperature scales were each invented independently by scientists working in different countries and contexts, and different ones caught on in different places before any international standardization happened.

This converter handles all seven historically significant temperature scales in one place. Whether you're checking weather forecasts from a different country, working on a science problem, or just satisfying genuine curiosity, type in any temperature and all seven equivalents appear simultaneously.

The Conversion Formulas

Every scale converts through Celsius as the common intermediate:

The only notable cross-conversion to memorize: −40 is the one temperature where Fahrenheit and Celsius are equal (−40°C = −40°F). This is also the point where the scales geometrically intersect if you draw them on a graph.

The Seven Scales Explained

Celsius (°C) was developed by Anders Celsius in 1742 and is used by nearly every country in the world for everyday temperature. The scale places water's freezing point at 0° and boiling point at 100° at sea-level atmospheric pressure — an intuitive, practical division.

Fahrenheit (°F) was developed by Daniel Gabriel Fahrenheit in 1724 and remains the official scale of the United States, Belize, and a few territories. Its reference points (32° for freezing, 212° for boiling) seem arbitrary because Fahrenheit originally calibrated against a brine solution. For human weather experience, the 0–100°F range maps loosely to "extreme cold" to "extreme heat," which some argue makes it intuitively useful for weather.

Kelvin (K) is the SI unit of thermodynamic temperature used in all scientific contexts. It starts at absolute zero — the theoretical minimum temperature where molecular motion ceases entirely (−273.15°C). Kelvin uses the same step size as Celsius, just offset. Physicists use Kelvin because it gives thermodynamically meaningful ratios: 200K is genuinely twice as much thermal energy as 100K.

Rankine (°R) is Kelvin's counterpart using Fahrenheit degree steps. It's primarily found in some American engineering fields, thermodynamics textbooks, and aerospace applications that work in imperial units.

Delisle (°De) was developed by Joseph-Nicolas Delisle in 1732 for the Russian Imperial Observatory. Its scale is inverted from common sense — boiling water is 0°De and colder temperatures are higher numbers. It was used in Russia for much of the 18th century and has no practical modern application.

Newton (°N) was Newton's personal attempt at a temperature scale in the early 1700s. Water freezes at 0°N and boils at 33°N. The 33-degree range for the water span is notably arbitrary. It was never widely adopted.

Réaumur (°Ré) was popular in France, Germany, and Russia during the 18th and early 19th centuries. Water freezes at 0°Ré and boils at 80°Ré. You'll encounter it in older European scientific literature and some historical cookbooks, which referenced cooking temperatures in Réaumur.

Useful Reference Points

Practical Use Cases

Reading international weather: Weather apps and international news often report temperatures in Fahrenheit (US) or Celsius (everywhere else). Convert quickly to understand what the forecast actually means.

Cooking with foreign recipes: Many American recipes specify oven temperatures in Fahrenheit. Conversion to Celsius is essential for anyone using a non-US oven (which typically has Celsius markings).

Scientific work: Physics, chemistry, and materials science all standardize on Kelvin. Thermodynamics problems require Kelvin for ratios and equations involving the ideal gas law (PV = nRT, where T must be in Kelvin).

Medical understanding: Normal body temperature is 37°C or 98.6°F. A fever threshold is typically 38°C / 100.4°F. Different medical traditions use different scales in documentation.

Calibrating sensors and instruments: Electronics and IoT projects often involve temperature sensors that output values in one scale which need to be displayed or logged in another.

Frequently Asked Questions

Why is there no negative Kelvin? Kelvin starts at absolute zero — zero molecular kinetic energy. You can't have less than no kinetic energy, so negative Kelvin is physically impossible in the conventional thermodynamic sense. (There are exotic quantum systems described as having "negative temperature," but that's a specific technical exception, not a general rule.)

Is 0°C exactly 32°F? Yes, by definition. The Celsius scale was calibrated to make 0° the freezing point of water at standard atmospheric pressure, and the Fahrenheit conversion formula is exact: 0°C = (0 × 9/5) + 32 = 32°F.

What's the hottest temperature ever recorded? For everyday weather, the world record air temperature is 56.7°C / 134.1°F (Death Valley, 1913). For laboratory physics, scientists have reached temperatures above 5 trillion°C in particle accelerators like the Large Hadron Collider — far hotter than the interior of the sun.