The Three Temperature Scales, at a Glance

Celsius and Fahrenheit are the two scales most people encounter daily — Celsius across most of the world, Fahrenheit mainly in the United States. Kelvin is the scientific standard, an absolute scale where 0 K represents the total absence of thermal energy. According to NIST, one Celsius degree is exactly equal in size to one kelvin — they're just offset by 273.15.

Conversion Formulas

This converter applies these exact formulas live — no rounding shortcuts, no approximations.

How to Use This Converter

Type a number into any one of the three fields — Celsius, Fahrenheit, or Kelvin — and the other two update instantly. There's no "Calculate" button needed; conversion happens as you type.

Why Fahrenheit and Celsius Disagree at -40

There's exactly one point where Celsius and Fahrenheit read the same number: −40° on both scales. Above and below that point, the two scales diverge in opposite directions because Fahrenheit degrees are smaller (180 degrees between freezing and boiling) than Celsius degrees (100 degrees over the same range).

Why Kelvin Has No Negative Numbers

Kelvin is an absolute scale anchored to absolute zero — the theoretical point where atomic motion stops entirely. Since nothing can be colder than that, Kelvin never goes negative, which is why scientists prefer it for physics and chemistry calculations where Celsius or Fahrenheit's arbitrary zero points would be misleading.

Common Conversion Touchpoints

• Cooking: most US recipes use Fahrenheit, most international recipes use Celsius
• Weather: the US, Belize, and a handful of territories use Fahrenheit; nearly everywhere else uses Celsius
• Science: lab work and physics almost always use Celsius or Kelvin, rarely Fahrenheit
• Medicine: normal human body temperature is about 37°C / 98.6°F / 310.15 K

Quick Reference Table

The table above the calculator covers the most commonly searched reference points — from absolute zero to a baking oven. Bookmark this page if you regularly convert oven temperatures or weather readings between scales.

Precision and Rounding

This converter calculates to full floating-point precision, then displays a reasonable number of decimal places. For scientific or engineering work requiring exact significant figures, always retain more decimal places than shown here and round only at your final reporting step.

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If you're working across multiple measurement systems, our general unit converter covers length, weight, and volume, while our currency converter handles exchange rates. For broader scientific calculations, check out our scientific calculator.

Frequently Asked Questions