Temperature Calculator
Temperature is a measure of thermal energy, expressed in several scales depending on context. Celsius (°C) is used in everyday life worldwide; Fahrenheit (°F) is used in the US; Kelvin (K) is the SI base unit used in science and engineering — it starts at absolute zero (−273.15°C). Rankine (°R) is the Fahrenheit-based absolute scale used in US engineering thermodynamics. Converting between scales requires simple formulas: °F = °C × 9/5 + 32; K = °C + 273.15; °R = (°C + 273.15) × 9/5. Temperature differences (ΔT) are the same magnitude in Celsius and Kelvin. Thermal expansion ΔL = α·L₀·ΔT quantifies how materials expand when heated.
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lightbulb Tips
- •°F = °C × 9/5 + 32 | °C = (°F − 32) × 5/9
- •Kelvin has same degree size as Celsius — ΔK = ΔC
- •−40°C = −40°F — the only crossover point
- •ΔL = α · L₀ · ΔT for thermal expansion
How to Use This Calculator
Choose Your Input Scale
Select Celsius, Fahrenheit, Kelvin, or Rankine as your starting scale from the tab row, then type your temperature value in the input field.
See All Conversions Instantly
All four scales update simultaneously as you type. Results are shown with full precision plus a visual thermometer context (freezing, body temp, boiling).
Calculate Temperature Difference
Switch to the Difference tab to find ΔT between two temperatures. Useful for HVAC, cooking, and engineering calculations.
Use Thermal Expansion
Switch to the Thermal Expansion tab to calculate how much a material grows or shrinks with temperature change. Choose from material presets or enter a custom expansion coefficient.
The Formula
The Celsius and Fahrenheit scales share the same degree size relationship: a change of 1°C equals a change of 1.8°F. To convert °C to °F: multiply by 9/5 (= 1.8) then add 32. Kelvin uses the same degree size as Celsius but starts at absolute zero, so K = °C + 273.15. Rankine is Kelvin scaled to Fahrenheit degrees: °R = K × 9/5. The special crossover point where both scales agree: −40°C = −40°F.
°F = °C×9/5+32 | K = °C+273.15 | °R = K×9/5 | ΔL = α·L₀·ΔT
lightbulb Variables Explained
- °C Degrees Celsius — water freezes at 0°C, boils at 100°C
- °F Degrees Fahrenheit — water freezes at 32°F, boils at 212°F
- K Kelvin — absolute temperature, 0 K = −273.15°C (absolute zero)
- °R Rankine — absolute scale based on Fahrenheit, 0°R = −459.67°F
- ΔT Temperature difference or change (°C or K)
- α Coefficient of linear thermal expansion (per °C or per K)
- L₀ Original length before heating (m, mm, or any length unit)
- ΔL Change in length due to temperature change
tips_and_updates Pro Tips
Quick mental conversion: °F to °C — subtract 32 then halve (rough). Exact: × 5/9. Example: 68°F → (68−32)/2 ≈ 18°C (exact: 20°C).
The only temperature where °C = °F is −40°. Both scales cross at exactly −40 degrees.
Kelvin and Celsius have the same degree size — so a temperature difference of 10°C is also a difference of 10 K.
Absolute zero (0 K = −273.15°C = −459.67°F) is the coldest possible temperature — all molecular motion stops.
For cooking: 180°C = 356°F (moderate oven). 200°C = 392°F. Rule of thumb: °C × 2 + 30 ≈ °F for oven temps.
Frequently Asked Questions
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Data sourced from trusted institutions
All formulas verified against official standards.