Temperature Calculator

Knowing a few anchor points makes temperature intuitive across scales:

• Absolute zero: -273.15°C / -459.67°F / 0K — the theoretical minimum where molecular motion ceases.
• Dry ice: -78.5°C / -109.3°F — used for shipping frozen goods.
• Water freezing: 0°C / 32°F — the defining point for Celsius.
• Room temperature: 20-22°C / 68-72°F — standard for scientific measurements and HVAC settings.
• Body temperature: 37°C / 98.6°F — though individual normals range from 36.1-37.2°C.
• Pasteurization: 72°C / 161.6°F — kills harmful bacteria in milk (held for 15 seconds).
• Water boiling: 100°C / 212°F at sea level — decreases approximately 1°F per 500 feet of elevation.

Oven temperatures typically range from 150°C/300°F (low) to 260°C/500°F (pizza/broiling).

Daniel Fahrenheit (1724) set his scale using three reference points: brine freezing at 0°F, water freezing at 32°F, and human body temperature at 96°F (later corrected to 98.6°F). The seemingly arbitrary numbers created a scale where most weather temperatures fall between 0-100°F, which Fahrenheit considered practical.

Anders Celsius (1742) chose a more logical basis: water's freezing point at 0° and boiling point at 100° (originally reversed, corrected by Carl Linnaeus).

Lord Kelvin (1848) created an absolute scale starting at absolute zero, maintaining Celsius-sized degrees — this makes it essential for gas law calculations (PV = nRT requires absolute temperature) and thermodynamic equations.

The Rankine scale (absolute, Fahrenheit-sized degrees) is occasionally used in US engineering.

Recipe temperature conversion is critical when using international cookbooks.

Common oven temperature conversions:

• 180°C = 350°F (standard baking)
• 200°C = 400°F (roasting)
• 220°C = 425°F (high-heat roasting)
• 230°C = 450°F (pizza)
• 150°C = 300°F (slow baking)

Gas mark conversion: Gas Mark 4 = 180°C = 350°F, with each mark representing roughly 14°C/25°F increment.

For candy making, precise temperatures are critical:

• Soft ball stage is 112-116°C (234-240°F)
• Hard ball is 121-130°C (250-266°F)
• Hard crack is 146-154°C (295-310°F)

Internal meat temperatures for food safety:

• Chicken 74°C/165°F
• Ground beef 71°C/160°F
• Pork 63°C/145°F with 3-minute rest
• Beef steaks can be served at 52°C/125°F (rare) to 71°C/160°F (well done) depending on preference

To convert Celsius to Fahrenheit, multiply the Celsius value by 9/5 (equivalently 1.8) and add 32: °F = (°C × 9/5) + 32. For example, 25°C = (25 × 1.8) + 32 = 77°F.

To reverse the process, subtract 32 first, then multiply by 5/9: °C = (°F − 32) × 5/9.

These ratios come from the fact that the interval between water's freezing and boiling points spans 100 Celsius degrees but 180 Fahrenheit degrees, giving the 180/100 = 9/5 ratio.

The Kelvin scale, defined by BIPM and the SI as the base unit of thermodynamic temperature, uses the same degree size as Celsius, so K = °C + 273.15.

100 degrees Celsius equals 212 degrees Fahrenheit, the boiling point of water at standard sea-level pressure. Applying °F = (°C × 9/5) + 32 gives (100 × 1.8) + 32 = 180 + 32 = 212°F.

On the Kelvin scale this is 373.15 K, and on the Rankine scale it is 671.67°R.

This anchor pairing — 0°C = 32°F (freezing) and 100°C = 212°F (boiling) — is the easiest way to sanity-check any conversion.

Note that boiling point drops with altitude: NIST notes atmospheric pressure decreases with elevation, lowering water's boiling point by roughly 1°F per 500 feet, so at high altitude water boils below 212°F.

To convert Kelvin to Celsius, subtract 273.15: °C = K − 273.15.

To reach Fahrenheit, convert to Celsius first, then apply °F = (°C × 9/5) + 32; combined, °F = (K − 273.15) × 9/5 + 32. For example, 300 K = 300 − 273.15 = 26.85°C = 80.33°F.

The Kelvin (symbol K, never "degrees Kelvin") is the SI base unit of temperature defined by the BIPM through the fixed value of the Boltzmann constant since the 2019 SI redefinition.

Because Kelvin and Celsius share the same degree magnitude, any temperature difference is numerically identical in both: a change of 10°C equals a change of 10 K.

The Kelvin scale is the SI base unit of thermodynamic temperature, starting at absolute zero — the point where classical molecular motion theoretically stops. Absolute zero equals 0 K = −273.15°C = −459.67°F.

Because Kelvin has no negative values and starts at true zero, it is required for gas-law and thermodynamic equations such as PV = nRT, where using Celsius or Fahrenheit would give wrong results.

NIST and the BIPM define the Kelvin through the fixed numerical value of the Boltzmann constant (1.380649 × 10⁻²³ J/K).

Common Kelvin reference points include:

• Water freezing at 273.15 K
• Room temperature near 293–295 K
• Body temperature at 310.15 K
• Water boiling at 373.15 K

Temperature conversion appears constantly across daily life and technical work:

• Travelers convert weather forecasts between Celsius and Fahrenheit when moving between the US and countries using the metric system.
• Home cooks translate oven settings from European recipes, where 180°C = 350°F is standard baking heat.
• Healthcare relies on precise readings: normal body temperature is 37°C = 98.6°F, and a fever is generally ≥ 38°C = 100.4°F.
• Scientists and engineers work in Kelvin for thermodynamics, cryogenics, and gas-law calculations, as standardized by the BIPM and the SI.
• HVAC technicians compute temperature differences (ΔT) for heating and cooling loads, and materials engineers use thermal expansion (ΔL = α·L₀·ΔT) to design bridges, railways, and pipelines that must tolerate seasonal temperature swings.

The Rankine scale (°R) is an absolute temperature scale that uses Fahrenheit-sized degrees, standing to Fahrenheit exactly as Kelvin stands to Celsius. It starts at absolute zero: 0°R = 0 K = −459.67°F.

To convert, use one of these:

• °R = °F + 459.67
• °R = K × 9/5
• °R = (°C + 273.15) × 9/5

For example, water freezing (0°C) equals 491.67°R, and water boiling (100°C) equals 671.67°R.

Rankine is used mainly in US engineering thermodynamics, where Fahrenheit degrees are conventional but an absolute scale is required for calculations. Like Kelvin, Rankine never takes negative values under normal conditions and is preferred wherever thermodynamic ratios matter.

A temperature difference (ΔT) is simply the change between two readings, and it is numerically identical in Celsius and Kelvin because both share the same degree size — so a drop from 30°C to 20°C is a ΔT of 10°C = 10 K. In Fahrenheit and Rankine, that same physical change equals 18°F = 18°R.

Temperature differences drive thermal expansion, calculated as ΔL = α·L₀·ΔT, where α is the material's coefficient of linear expansion (per K), L₀ is the original length, and ΔL is the length change.

For instance, steel with α ≈ 12 × 10⁻⁶ /K expands about 0.12 mm per meter for each 10 K rise. Engineers use this to size expansion joints in bridges and rail tracks.

The most frequent conversion errors are easy to avoid once you know them:

• Forgetting the +32 offset — the Celsius and Fahrenheit scales do not share a zero point, so you cannot simply multiply by 1.8. Always add 32 when going to Fahrenheit and subtract 32 first when going the other way.
• Applying the offset to temperature differences — a ΔT should use only the 9/5 ratio (or none for °C↔K), never +32.
• Writing "degrees Kelvin" or using a degree symbol with K — per the SI and BIPM, the correct form is just "kelvin" and "K".
• Rounding 273.15 to 273 for Kelvin — this introduces small errors in precise scientific work; retain the full 273.15 offset for accuracy.