Temperature Converter
Convert a single temperature reading between Celsius, Fahrenheit, Kelvin, and Rankine, or convert a temperature change (ΔT) between Celsius/Kelvin-sized degrees and Fahrenheit/Rankine-sized degrees. Results come with a visual comparison, a plain-language explanation, and a full step-by-step solution.
Background
Converting a single temperature and converting a change in temperature are not the same math. Absolute conversions (like 100°C → 212°F) need an offset because the scales start at different zero points. Temperature-change conversions (like "it rose 80 Celsius-degrees") never use an offset — only a scaling factor — because you're measuring a size, not a position. Mixing these up is one of the most common mistakes in chemistry and physics problems involving heat and calorimetry.
How to use this calculator
- Choose Convert a Reading for a single temperature (e.g., "20°C is what in °F?").
- Choose Convert a Change (ΔT) for a rise or drop in temperature (e.g., "an 80°C rise is how many °F?").
- For a change, optionally add a starting temperature and direction to see the actual start/end values.
- Click Calculate to see the visual, the converted values, and a full step-by-step explanation.
How temperature conversion works
Converting a single temperature needs an offset as well as a scale factor, because Celsius and Fahrenheit start counting from different zero points: °F = °C × 9/5 + 32.
Kelvin and Rankine are absolute scales — they start at true zero (absolute zero, where atomic motion is at its minimum) rather than an arbitrary point like water freezing.
Converting a change in temperature (ΔT) never uses an offset — only a scale factor — because a change is a size, not a position on the scale. This is the single most common mixup in heat and calorimetry problems.
A Fahrenheit degree is smaller than a Celsius degree: 180 Fahrenheit-sized degrees span the same range as 100 Celsius-sized degrees, so 1°C of change always equals exactly 1.8°F of change.
Celsius-sized degrees and Kelvin-sized degrees are identical in size (they just start at different zero points); the same is true of Fahrenheit-sized and Rankine-sized degrees.
Nothing can be colder than 0 K (absolute zero, −273.15°C) — this calculator rejects any input or result that would fall below it.
Formulas & Equations Used
Fahrenheit from Celsius: °F = °C × 9/5 + 32
Celsius from Fahrenheit: °C = (°F − 32) × 5/9
Kelvin: K = °C + 273.15
Rankine: °R = °F + 459.67 = K × 9/5
Change in Fahrenheit-sized degrees: ΔT(°F) = ΔT(°C) × 9/5 (no offset)
Change in Celsius-sized degrees: ΔT(°C) = ΔT(°F) × 5/9 (no offset)
Example Problems & Step-by-Step Solutions
Example 1 — Absolute conversion
Water boils at 100°C at sea level. Find this in Fahrenheit and Kelvin.
Step: °F = 100 × 9/5 + 32 = 180 + 32. K = 100 + 273.15.
Result: 212°F and 373.15 K.
Example 2 — Starting from Fahrenheit
Human body temperature is 98.6°F. Find this in Celsius and Kelvin.
Step: °C = (98.6 − 32) × 5/9 = 66.6 × 5/9. K = 37.0 + 273.15.
Result: 37.0°C and 310.15 K.
Example 3 — An extreme value
The Sun's surface is about 5,778 K. Find this in Celsius and Fahrenheit.
Step: °C = 5,778 − 273.15 = 5,504.85. °F = 5,504.85 × 9/5 + 32.
Result: 5,504.85°C and 9,940.73°F.
Example 4 — Temperature change (ΔT)
A pot of water is heated from 20°C to 100°C. What is the change in Fahrenheit-sized degrees?
Step: ΔT(°C) = 100 − 20 = 80°C. ΔT(°F) = 80 × 9/5.
Result: 144°F of change — check: 212°F − 68°F = 144°F ✓.
Example 5 — Rankine (engineering scale)
Convert 500 K to Rankine.
Step: °R = 500 × 9/5.
Result: 900°R.
Example 6 — Why ΔT never uses an offset
A day warms from 44°F to a record −56°F drop (Loma, Montana, 1972) — a 100°F swing.
Step: ΔT(°C) = 100 × 5/9 ≈ 55.6°C. No +32 or −273.15 offset appears anywhere — only the 5/9 scale factor.
Result: A 100°F swing equals about 55.6°C of change, not a converted position on the scale.
Frequently Asked Questions
What's the difference between converting a temperature and converting a change?
Converting a temperature needs an offset because Celsius and Fahrenheit start at different zero points. Converting a change in temperature only needs a scale factor, since it measures a size rather than a position on the scale.
Why does 1°C not equal 1°F?
A Fahrenheit degree is smaller: 180 Fahrenheit-sized degrees span the same range as 100 Celsius-sized degrees, so 1°C of change equals 1.8°F of change.
What is Rankine, and who uses it?
Rankine is an absolute scale, like Kelvin, but sized in Fahrenheit-sized degrees. It shows up mainly in some U.S. engineering and thermodynamics contexts.
Why can't a temperature go below 0 K?
0 Kelvin, or absolute zero, is the theoretical point where atomic motion is at its minimum. Nothing can be colder, so values below it are rejected as inputs and as results.
Why do very hot values switch to a ratio comparison instead of a scale bar?
A linear scale stretching from absolute zero to thousands of degrees would squeeze everyday reference points like body temperature and boiling water into an unreadable sliver. Above about 1,000°C, this calculator switches to Kelvin-based ratio comparisons instead, which stay meaningful at any scale.
Can I enter a negative value for the size of a temperature change?
Enter the size of the change as zero or a positive number, then use the direction option (up or down) if a starting temperature is also known. Keeping size and direction separate avoids sign confusion.
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