Temperature Converter — Fahrenheit, Celsius, Kelvin

°F to °C: (F − 32) × 5/9
°C to °F: (C × 9/5) + 32
°C to K:   C + 273.15
K to °C:   K − 273.15

Key reference points:
−40°: F and C are equal
0°C = 32°F (water freezes)
100°C = 212°F (water boils)
37°C = 98.6°F (body temperature)

Celsius and Fahrenheit are equal at exactly -40 degrees. The Kelvin scale starts at absolute zero (-273.15°C) — the coldest theoretically possible temperature.

F to C

=(A1-32)*5/9

C to F

=A1*9/5+32

C to K

=A1+273.15

Temperature Conversion ExplainedSearch YouTube tutorials →

Why Three Different Scales Exist

The Fahrenheit scale was developed by Daniel Gabriel Fahrenheit in 1724, using the freezing point of a saltwater brine (0°F) and human body temperature (~96°F, later adjusted to 98.6°F) as reference points. The resulting scale placed water's freezing at 32°F and boiling at 212°F — not round numbers, but the scale spread over a range that many find intuitive for weather (0°F = very cold, 100°F = very hot).

The Celsius scale (1742) was designed around water — 0°C freezes, 100°C boils at sea level — creating a logical, decimal-friendly scale. It was adopted as the scientific and international standard, used in weather forecasting everywhere except the US, and in all scientific contexts worldwide.

The Kelvin scale (1848), developed by Lord Kelvin, is the absolute temperature scale. Zero Kelvin (absolute zero) is -273.15°C — the coldest possible temperature where molecular motion ceases. One Kelvin degree equals one Celsius degree in magnitude; the scales differ only in their starting point. Kelvin is essential for physics and chemistry because many equations require absolute temperature.

Quick Mental Conversion Tricks

For Celsius to Fahrenheit quickly: double the Celsius temperature and add 30. This gives a close approximation — 20°C → (20×2)+30 = 70°F (actual: 68°F). For Fahrenheit to approximate Celsius: subtract 30 and halve. 80°F → (80-30)/2 = 25°C (actual: 26.7°C).

One exact shortcut: -40° is the same in both Fahrenheit and Celsius. Starting from that anchor: each 5°C equals 9°F. So 0°C = -40 + 40°C = -40 + 72°F = 32°F. This anchor point lets you derive other conversions mentally rather than memorizing the formula.

Frequently Asked Questions

Inertia, primarily. The US adopted Fahrenheit early and never made the systemic transition to Celsius that most other English-speaking countries made in the 1960s-70s. Multiple legislative efforts to officially metricate the US have failed due to the high short-term costs of conversion and resistance to changing familiar conventions. Interestingly, US scientific, medical, and military contexts use Celsius and metric units.

0 Kelvin = -273.15°C = -459.67°F. It is the lowest possible temperature — the point where atoms reach minimum quantum energy state. It cannot actually be reached (only approached asymptotically), but scientists have achieved temperatures within billionths of a degree of it. The third law of thermodynamics states that absolute zero is unattainable.

Many physical laws relate quantities to absolute temperature. Ideal gas law PV = nRT requires absolute temperature — if you used Celsius, a 0°C gas would appear to have zero pressure or volume, which is wrong. The Kelvin scale starts at true zero, making all temperatures positive and ensuring equations work correctly.

At exactly -40 degrees, both scales give the same reading. The two temperature scales cross because Fahrenheit has a different zero point and a different degree size — they're two linear functions of temperature that happen to intersect at -40.