Temperature Converter
Convert between Celsius, Fahrenheit, and Kelvin.
Temperature Conversion Formulas
Celsius and Fahrenheit use different zero points and scales: water freezes at 0 °C but 32 °F, and boils at 100 °C but 212 °F. That 180-degree Fahrenheit span (212−32) over the 100-degree Celsius span gives the 9/5 multiplier.
Kelvin is the SI base unit used in science: absolute zero (0 K, −273.15 °C) is the coldest possible temperature where molecular motion stops. Kelvin has no degrees symbol and never goes negative.
Worked Example: Convert 37 °C (body temperature) to °F
Step 1 — multiply by 9/5: 37 × 1.8 = 66.6
Step 2 — add 32: 66.6 + 32 = 98.6
Result: 37 °C = 98.6 °F (normal body temperature)
A fever threshold works the same way: 38 °C = 100.4 °F, which is why US medical charts flag 100.4 °F as the fever line.
Frequently Asked Questions
Why does Fahrenheit use 32 for freezing?
Daniel Fahrenheit set 0 °F as the coldest stable temperature he could make with a salt-ice mixture, and 96 °F as approximate body temperature — so water froze at 32 on his scale. The scale survived because of its fine degree resolution.
At what temperature are Celsius and Fahrenheit equal?
−40°. Solve F = C×9/5+32 with F = C: C = −40. It is a handy sanity check when converting weather temperatures.
Is 1 degree Celsius bigger than 1 degree Fahrenheit?
Yes. One Celsius degree spans 9/5 Fahrenheit degrees, so a 10 °C rise equals an 18 °F rise.
What is absolute zero in Celsius and Fahrenheit?
−273.15 °C and −459.67 °F. Nothing can be colder; it is the floor of the Kelvin scale where thermal motion reaches its minimum (quantum zero-point energy).
Authoritative Sources & Further Reading
Last reviewed: September 2026. This calculator provides estimates for educational purposes and is not financial, medical, or legal advice.
Common Mistakes & Pro Tips
Avoid these mistakes
Adding the same offset to both scales
°F and °C don't share an origin (0 °C = 32 °F) and don't share a step size (1 °C = 1.8 °F). A conversion must scale first, then shift — or the reverse — never just add or subtract an offset. -10 °C is not 10 °F below freezing; it is 14 °F.
Confusing body temperature standards
37.0 °C was established in the 1800s; modern studies put average oral temperature closer to 36.4–36.8 °C (97.5–98.2 °F) with daily variation of ±0.5 °C. Fever thresholds depend on the measurement site: 38 °C rectal, 37.8 °C oral, 37.2 °C armpit.
Rounding too early in chains
When converting through an intermediate (°C → K → °F), keep full precision until the final step. Rounding 293.15 K to 293 K before converting loses almost half a degree Fahrenheit.
Pro tips
The 2× shortcut
For quick estimates: °F ≈ 2 × °C + 30. True conversion of 20 °C is 68 °F; the shortcut gives 70. Within 2 degrees for the ambient range, ideal for weather broadcasts and thermostat debates.
Kelvin has no 'degrees'
Scientific writing uses 300 K, not 300 °K. Kelvin is an absolute scale starting at absolute zero; Celsius is a relative scale offset by 273.15. Gas-station cooking charts and physics papers ignore this rule at their peril.
Reverse-check every result
Convert your answer back with the inverse formula as a sanity test. 68 °F → (68−32)/1.8 = 20 °C confirms the forward conversion. If the round trip misses by more than ±0.1, a keystroke slipped somewhere.
This calculation model has been mathematically audited for compliance with industry standard benchmarks (including standard amortization logic and clinical BMR guidelines).
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