Temperature Converter

Temperature Reference Guide

Conversion Formulas

Converting between temperature scales uses straightforward formulas once you know them. Celsius to Fahrenheit: multiply by 9/5 (i.e. 1.8), then add 32 — so 20°C = 20 × 1.8 + 32 = 68°F. Fahrenheit to Celsius reverses this: subtract 32 first, then multiply by 5/9 — so 98.6°F = (98.6 − 32) × 5/9 = 37°C. For the Kelvin scale (used in science), the conversion is simpler because Kelvin uses the same degree size as Celsius: Celsius to Kelvin just add 273.15, and Kelvin to Celsius subtract 273.15. A few anchor points are worth memorising for quick mental checks: water freezes at 0°C = 32°F = 273.15 K, water boils at 100°C = 212°F = 373.15 K, and normal body temperature is 37°C = 98.6°F. A handy quick estimate for Celsius to Fahrenheit is 'double it and add 30' (20°C → about 70°F), which is close enough for weather. The −40 point is a curiosity: −40°C equals exactly −40°F, the one temperature where the two scales meet. This calculator handles all conversions precisely, but knowing the anchor points lets you sanity-check any result at a glance.

Cooking Temperatures

Temperature conversion comes up constantly in the kitchen, especially with recipes that mix Celsius, Fahrenheit, and gas marks. Useful reference points: a fridge should be 3–5°C, a freezer −18°C. Oven temperatures: a low oven is around 150°C (300°F, gas mark 2), moderate is 180°C (350°F, gas mark 4), and hot is 220°C (425°F, gas mark 7). Water boils at 100°C (212°F), and deep frying is typically done at 170–190°C. For sweet-making, sugar syrup passes through stages by temperature — soft ball at about 112–116°C, hard ball around 121–130°C, and hard crack at 149–154°C — which is why a sugar thermometer matters for confectionery, and caramel forms around 170°C. Meat safety relies on internal temperature: poultry should reach 74°C, and these targets are about food safety, not preference. Remember that fan (convection) ovens run hotter than conventional, so most recipes suggest reducing the stated temperature by about 20°C for a fan oven. When converting a recipe, convert the oven temperature first and check it against these familiar reference points to catch any error.

Scientific Reference Points

Beyond everyday temperatures, some scientific reference points help contextualise readings and demonstrate the range of temperatures in nature. The coldest possible temperature is absolute zero, −273.15°C (0 K), where molecular motion theoretically stops — nothing can be colder, which is why the Kelvin scale starts there. Liquid nitrogen boils at −196°C and is used to freeze things rapidly in labs and medicine. Dry ice (solid carbon dioxide) sits at −78.5°C and sublimes directly from solid to gas. Moving up: water freezes at 0°C and boils at 100°C (at sea level — boiling point drops at altitude due to lower pressure). The human body runs at 37°C, with a fever typically above 38°C. A typical oven reaches 200–250°C, and a wood fire burns around 600°C. The surface of the Sun is about 5,500°C, and its core millions of degrees. These reference points span an enormous range and help you judge whether a reading is plausible. The Kelvin scale is preferred in science because it has no negative values and is proportional — doubling the Kelvin temperature doubles the average molecular energy, which isn't true for Celsius or Fahrenheit.

Units and Significant Figures

Temperature conversions are usually exact arithmetic, but a few points avoid errors. The Celsius-Fahrenheit conversion involves both a scaling factor (9/5) and an offset (32), so you must apply them in the right order: for C to F, multiply by 9/5 first, then add 32; reversing the order gives the wrong answer. The Kelvin conversion only involves an offset (273.15) because a one-degree change is the same size in Celsius and Kelvin — this is why temperature differences (not absolute temperatures) are the same number in °C and K. When converting, watch significant figures: body temperature quoted as 37°C converts to 98.6°F, but quoting 98.60000°F implies false precision. In scientific work, temperatures are usually given in Kelvin, and many gas-law and thermodynamics formulas require Kelvin (using Celsius gives wrong results because those formulas assume an absolute scale starting at zero). A common mistake in physics is forgetting to convert to Kelvin before applying such formulas. For everyday use, rounding to the nearest degree is fine; for scientific or medical contexts, match the precision of your measuring instrument and remember that the scale you use (especially Kelvin vs Celsius) can change whether a formula works at all.