Instantly convert between Fahrenheit, Celsius, Kelvin, Rankine, Délisle, Newton, Réaumur, and Rømer. Real-time results for all 8 temperature scales.
In the United States, Fahrenheit (°F) is the everyday unit: weather forecasts, home thermostats, oven dials, and body-temperature readings all use °F. Daniel Gabriel Fahrenheit — a German-Polish physicist working in Amsterdam — published his scale in 1724, setting 32 °F as the freezing point of water and 212 °F as the boiling point. He was directly inspired by Ole Rømer's earlier thermometer, which he had visited in Copenhagen in 1708. The Fahrenheit scale was the dominant scientific standard in the English-speaking world until the 20th century, when Celsius and Kelvin became the global norm in science and medicine.
Unlike linear unit conversions (feet to inches), temperature conversion is an affine transformation: each scale has its own zero point and a different degree size. Simply multiplying by one constant factor is not enough — you must also add or subtract an offset. This converter uses Celsius as the intermediate step and automatically applies the correct two-step affine formula for every scale.
Every conversion passes through Celsius as a pivot point. First the input value is converted to Celsius using the toC formula, then that Celsius value is converted to the target scale using the fromC formula. The general structure is:
Where f_toC converts the source scale to Celsius and f_fromC converts Celsius to the result. Detailed formulas for each scale are shown in the panels below.
→ Celsius (input)
Celsius → (output)
Key reference values
Furnace Creek in Death Valley, California holds the world record: 134 °F (56.7 °C, 329.85 K) on July 10, 1913. For international visitors used to Celsius: 56.7 °C is a figure that exceeds even the hottest European or Middle-Eastern city records and represents a level of heat lethal to unprotected humans within minutes.
The classic American reference of 98.6 °F is the Fahrenheit equivalent of exactly 37 °C (310.15 K), the normal human core temperature established by German physician Carl Reinhold August Wunderlich in 1851. Today most U.S. physicians recognize a normal range of 97–99 °F (36.1–37.2 °C). A fever begins above 100.4 °F (38 °C).
American recipes almost always specify oven temperatures in Fahrenheit. Chocolate chip cookies bake at 375 °F (190.6 °C, 463.7 K). Roast turkey cooks at 325–350 °F (163–177 °C). Pizza in a home oven goes at 450–500 °F (232–260 °C). When a European recipe gives Celsius or Gas Mark numbers, this converter provides the correct Fahrenheit value instantly.
Absolute zero, 0 K = −459.67 °F = −273.15 °C = 0 °R, is the lowest theoretically possible temperature, at which all classical thermal motion of atoms ceases. It was defined by Lord Kelvin (William Thomson) at the University of Glasgow in 1848. In American thermodynamic engineering, absolute temperatures are often expressed in Rankine (°R) — the Fahrenheit-based absolute scale, where 0 °R = absolute zero and 1 °R = 1 °F.
Type the numeric temperature value you want to convert into the input field. Positive, negative, and decimal numbers are all accepted.
Select the source scale from the dropdown menu. All 8 scales are listed with their full name and symbol.
The converter first calculates the Celsius equivalent (toC formula), then applies the fromC formula for every target scale.
Results are grouped into: Common scales (Celsius, Fahrenheit, Kelvin, Rankine) and Historical scales (Délisle, Newton, Réaumur, Rømer).
All values update in real time as you type — no confirm button needed. Very large or small values are shown in scientific notation.
Quick mental estimate Fahrenheit → Celsius: subtract 32, then divide by 2 (approximate). Exact formula: °C = (°F − 32) × 5/9. So 98.6 °F = exactly 37 °C. The reverse: °F = °C × 9/5 + 32.
Kelvin drops the degree symbol — write 'K', never '°K'. One kelvin is the same size as one Celsius degree; the only difference is the zero point (shifted by 273.15 units). Kelvin is the SI base unit used in all scientific and engineering absolute-temperature calculations.
The Rankine scale is Fahrenheit's absolute counterpart: 0 °R = absolute zero, and one Rankine degree equals one Fahrenheit degree. Conversion: °R = °F + 459.67. Rankine is still used in some U.S. aeronautical and thermodynamic engineering fields.
The Délisle scale works backwards: larger values correspond to lower temperatures. Water boils at 0 °De and freezes at 150 °De — the exact opposite of Celsius. It was invented by Joseph-Nicolas Delisle in 1732 and used in Russian observatories for decades.
Fahrenheit and Celsius cross at exactly −40°: −40 °F = −40 °C. That is the single intersection of the two linear scales — a useful party fact for Americans visiting countries that use Celsius.
Most unit conversions are linear: one foot is always 12 inches. But temperature scales have different zero points — 0 °F is not the same physical state as 0 °C (which is 32 °F above water's freezing point) or 0 K (absolute zero). Because the zeros don't align, a scaling factor alone is not sufficient; an offset (addition or subtraction) is also required. This makes temperature conversion an affine transformation, not a purely proportional one.
Kelvin and Celsius have the same degree size (1 K = 1 °C as an interval), but different zero points. 0 °C = 273.15 K (ice melting point). 0 K = −273.15 °C (absolute zero). Kelvin is the SI base unit for thermodynamic temperature, used wherever absolute values are needed — physics, chemistry, and engineering worldwide.
The two scales are equal at exactly −40°: −40 °F = −40 °C. That is the only intersection of the two straight lines, because only there do the factor 9/5 and offset +32 mathematically cancel each other out.
Fahrenheit was adopted in the British colonies in the early 18th century, before the metric system existed. It became deeply embedded in American culture across weather, cooking, and healthcare. Despite the rest of the world switching to Celsius after the mid-20th century, the US never fully transitioned. In science, medicine, and industry, the US already uses Celsius and Kelvin — Fahrenheit persists mainly in everyday consumer contexts.
Rankine (°R) was developed by Scottish engineer William Rankine in 1859 as the absolute equivalent of Fahrenheit. It is used in some U.S. aeronautical engineering, gas dynamics, and older HVAC standards — fields where absolute temperature is necessary but engineers prefer Fahrenheit-sized degrees. Outside the US, Rankine has essentially no practical use.
Daniel Gabriel Fahrenheit (1686–1736) built his scale in 1724 around three fixed points: a salt-water ice-brine mixture (0 °F, the coldest thing he could reliably reproduce), the freezing point of pure water (32 °F), and human body temperature (96 °F in his original scale, later adjusted to 98.6 °F). He was inspired by Ole Rømer's thermometer, which used water and blood as calibration points, and he scaled his readings by a factor of 4 to reduce fractional readings.
All conversions are calculated using exact affine formulas. Values are rounded to 8 significant figures for display. For scientific or engineering precision work, always verify results with calibrated instruments.