Temperature Converter — Celsius, Fahrenheit, and Kelvin
Temperature is measured in different scales depending on context — Celsius for everyday use in most of the world, Fahrenheit in the United States, and Kelvin in science. Converting between them requires different formulas for each pair of scales. The free temperature converter on PublicSoftTools converts between all three scales instantly, with formulas, reference temperatures, and a complete conversion table.
How to Convert Temperatures
- Open the temperature converter.
- Enter a temperature value in any scale: Celsius (°C), Fahrenheit (°F), or Kelvin (K).
- The equivalent temperatures in all other scales update instantly.
- See the step-by-step calculation showing which formula was applied.
Temperature Conversion Formulas
| From | To | Formula | Reverse | Example |
|---|---|---|---|---|
| Celsius (°C) | Fahrenheit (°F) | °F = (°C × 9/5) + 32 | °C = (°F − 32) × 5/9 | 20°C → (20 × 9/5) + 32 = 36 + 32 = 68°F |
| Celsius (°C) | Kelvin (K) | K = °C + 273.15 | °C = K − 273.15 | 100°C → 100 + 273.15 = 373.15 K |
| Fahrenheit (°F) | Kelvin (K) | K = (°F − 32) × 5/9 + 273.15 | °F = (K − 273.15) × 9/5 + 32 | 32°F → (32 − 32) × 5/9 + 273.15 = 273.15 K |
Reference Temperature Table
| Event / reference | Celsius | Fahrenheit | Kelvin | Notes |
|---|---|---|---|---|
| Absolute zero | −273.15°C | −459.67°F | 0 K | Coldest theoretically possible temperature; no molecular motion |
| Liquid nitrogen (boiling point) | −195.79°C | −320.42°F | 77.36 K | Used for cryogenic storage, food freezing demonstrations |
| Dry ice (CO₂ sublimation) | −78.5°C | −109.3°F | 194.65 K | Solid CO₂ turns directly to gas (sublimation) |
| Water freezes (at 1 atm) | 0°C | 32°F | 273.15 K | Defines 0°C in the Celsius scale (originally melting point of ice) |
| Body temperature (normal) | 37°C | 98.6°F | 310.15 K | Normal human core temperature. Fever: above 38°C / 100.4°F |
| Water boils (at 1 atm) | 100°C | 212°F | 373.15 K | Defines 100°C in the Celsius scale. Lower at altitude (lower pressure). |
| Autoclave sterilisation | 121°C | 249.8°F | 394.15 K | Standard sterilisation temperature for medical equipment at 15 psi |
| Baking (moderate oven) | 180°C | 356°F | 453.15 K | Gas mark 4; typical baking temperature |
| Iron melting point | 1,538°C | 2,800°F | 1,811 K | Pure iron; steel melts at slightly lower temperatures |
| Surface of the Sun | 5,500°C | 9,932°F | 5,773 K | Photosphere surface temperature; core is ~15 million K |
The Three Temperature Scales Explained
Celsius (°C)
Devised by Anders Celsius in 1742 and adopted in most of the world as the standard everyday temperature scale. The Celsius scale is defined by two fixed reference points: 0°C = water freezes at 1 atmosphere pressure; 100°C = water boils at 1 atmosphere pressure. The degree spacing is identical to Kelvin — a change of 1°C equals a change of 1 K.
Fahrenheit (°F)
Developed by Daniel Gabriel Fahrenheit in 1724. Originally defined with 0°F as the temperature of a brine solution and 96°F as human body temperature. In the modern definition: 32°F = water freezes, 212°F = water boils, with 180 degrees between these points. Used primarily in the United States for everyday temperatures. US scientific work uses Celsius and Kelvin like the rest of the world.
Kelvin (K)
The SI unit of temperature. Defined with 0 K (absolute zero) as the lowest theoretically possible temperature — the point at which all molecular motion ceases. There are no negative Kelvin temperatures. The scale has the same degree spacing as Celsius: 0 K = −273.15°C; 273.15 K = 0°C. Kelvin is used in thermodynamics, astronomy, physics, chemistry, and any scientific context where temperature must be expressed as an absolute quantity. The unit is written K, not °K.
Quick Mental Conversion Shortcuts
For everyday purposes, these approximate rules work well:
- Celsius to Fahrenheit (rough): Double the Celsius temperature and add 30. Error ≤ 2°F in the −10°C to 35°C range. Example: 20°C × 2 + 30 = 70°F (exact: 68°F).
- Fahrenheit to Celsius (rough): Subtract 30, then halve. Example: 100°F → (100 − 30) ÷ 2 = 35°C (exact: 37.8°C).
- Useful exact points to remember: 0°C = 32°F; 10°C = 50°F; 20°C = 68°F; 30°C = 86°F; 37°C = 98.6°F; 100°C = 212°F.
The temperatures 40°C = 104°F is a useful reference: a temperature above 40°C (104°F) is dangerously hot — both for fever (medical emergency) and for outdoor environments.
Temperature in Cooking
UK ovens traditionally use Gas Marks (1–9); US and European ovens use Fahrenheit or Celsius. Common cooking temperatures:
- Very slow / warm: 120°C / 250°F / Gas Mark ½
- Slow / low: 150°C / 300°F / Gas Mark 2
- Moderate: 180°C / 350°F / Gas Mark 4 (most baking)
- Moderately hot: 190°C / 375°F / Gas Mark 5
- Hot: 220°C / 425°F / Gas Mark 7
- Very hot: 240°C / 475°F / Gas Mark 9
Temperature and Weather Contexts
Understanding temperature scales matters for weather contexts:
- UK weather ranges: −10°C (14°F) severe cold; 0–10°C (32–50°F) cold; 10–20°C (50–68°F) mild; 20–30°C (68–86°F) warm; 30°C+ (86°F+) hot
- US conversions: 0°F = −17.8°C (very cold); 32°F = 0°C (freezing); 72°F = 22.2°C (comfortable room temperature); 100°F = 37.8°C (hot day)
- UK record high: 40.3°C (104.5°F) recorded at Coningsby, Lincolnshire on 19 July 2022
- UK record low: −27.2°C (−17°F) recorded at Braemar, Scotland
Common Questions
Is there a temperature where Celsius and Fahrenheit are equal?
Yes — exactly −40°. At −40°C = −40°F, both scales give the same reading. This is the only temperature where Celsius and Fahrenheit values are identical. You can derive this by setting the conversion equation equal: °F = °C → (°C × 9/5) + 32 = °C → solving gives °C = −40.
Why does the US use Fahrenheit?
The Fahrenheit scale was the dominant temperature scale in English-speaking countries until the adoption of the metric system. The US has not adopted the metric system for everyday use, so Fahrenheit persists for weather, cooking, and body temperature contexts. US science, medicine (internationally published research), and engineering use Celsius and Kelvin. The US is one of only three countries — along with Liberia and Myanmar — that have not officially adopted the metric system.
What is the hottest temperature ever recorded?
For natural environments: 56.7°C (134.1°F), recorded at Furnace Creek in Death Valley, California, on 10 July 1913 — though some meteorologists dispute this measurement. The highest reliably verified temperature is 54.4°C (130°F), recorded multiple times in Death Valley in recent years. For engineered environments: the Large Hadron Collider creates quark-gluon plasma at around 5.5 trillion kelvin (5.5 × 10¹² K) — hotter than the Big Bang.
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Instantly convert between Celsius, Fahrenheit, and Kelvin with conversion formulas and a complete reference table.
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