Temperature Interval Converter: ΔK, Δ°C, Δ°F & More
Convert temperature differences (ΔT)—not absolute temperatures. Essential for heat transfer, thermal expansion, and specific heat.
Convert temperature intervals between kelvin, degree Celsius, degree Fahrenheit, degree Rankine, and degree Reaumur. One Δ°C = one K; one Δ°F = 5/9 K. Use this for ΔT in formulas—use a temperature converter for absolute values like 32°F to °C.
What is a temperature interval?
A temperature interval is a difference between two temperatures (ΔT). It’s not a reading on a thermometer—it’s “how many degrees did it change?” That matters because the size of one degree depends on the scale: one degree Celsius equals one kelvin, but one degree Fahrenheit is only 5/9 of a kelvin. So a change of 20°C is a change of 20 K, but a change of 20°F is a change of about 11.1 K.
Many sites get this wrong by using a standard temperature converter for intervals. Converting 20°C to Fahrenheit gives 68°F (absolute). Converting a change of 20°C gives a change of 36°F. This tool is built for the latter—intervals only.
How interval conversion works
All intervals are normalized to kelvin (K). The relationship between interval sizes:
Degree Rankine matches Fahrenheit (1 °R = 5/9 K). Reaumur: 1 °r = 1.25 K. Multiply your interval by the source unit’s factor to get K, then divide by the target unit’s factor to get the result. Example: 10 Δ°F → 10 × (5/9) ≈ 5.56 K → 5.56 Δ°C.
When to use intervals vs absolute temperature
Use interval conversion whenever a formula calls for ΔT: heat transfer (q = k·A·ΔT/L), thermal expansion (ΔL = α·L·ΔT), specific heat (Q = m·c·ΔT), or U-value (q = U·A·ΔT). The formula cares about the difference, not whether you started at 0°C or 100°C.
Use a temperature converter when you need an absolute reading in another scale—e.g. “what is 32°F in Celsius?” (0°C) or “what is 100°C in Kelvin?” (373.15 K). Those are points on the scale, not differences.
Common conversions at a glance
| From | To | Formula |
|---|---|---|
| Δ°C | ΔK | × 1 |
| Δ°F | ΔK | × 5/9 |
| Δ°F | Δ°C | × 5/9 |
| Δ°r | ΔK | × 1.25 |
Avoiding common mistakes
The biggest mistake is using a regular temperature converter for a change in temperature. 20°C as an absolute temp is 68°F; a change of 20°C is a change of 36°F. Always ask: “Am I converting a reading or a difference?” Degree Celsius and degree centigrade are the same for intervals (both 1 = 1 K). Rankine and Fahrenheit have the same interval size (5/9 K).
Temperature Interval FAQ
? Why is 1 Δ°C = 1 K but 1°C ≠ 1 K?
As intervals, one degree Celsius and one kelvin are the same size—they’re both 1/100 of the span between water’s freezing and boiling at 1 atm. So a change of 10°C equals a change of 10 K. As absolute temperatures, 1°C = 274.15 K (different zero point). This converter is for intervals only.
? How do I convert a temperature change from °F to °C?
Multiply the change in °F by 5/9 to get the change in °C. So a 18°F rise is a 10°C rise. Don’t use the “add 32, multiply by 5/9” formula—that’s for absolute temperature. For intervals, it’s just the scale factor 5/9.
? What is degree Reaumur?
Reaumur (°r) uses 0°r at water’s freezing point and 80°r at boiling (1 atm). So one °r = 100/80 = 1.25 K (or 1.25 °C as an interval). It’s rarely used today but appears in some European historical or specialty contexts. This converter includes it for completeness.
? When do I use temperature interval instead of absolute temperature?
Use intervals (Δ°C, ΔK, Δ°F) for temperature changes—specific heat (Q = mcΔT), thermal expansion (ΔL = αLΔT), or heat transfer. Use absolute temperature for ideal gas law, saturation pressure, or “what is the temperature?” This converter is for intervals only; use the Temperature converter for absolute °C, °F, K.
? How do I convert temperature difference from Kelvin to Fahrenheit?
Multiply the change in K by 9/5 (or 1.8) to get the change in °F. So 10 K = 18 °F. Don’t add 32—that’s for absolute temperatures. For intervals, only the scale ratio matters. Use the converter above for Δ°C, Δ°R, Δ°r as well.
? What is degree Rankine (°R) for temperature intervals?
As intervals, one degree Celsius and one kelvin are the same size. As absolute readings, 0°C = 273.15 K, so “1°C” as a temperature is 274.15 K. This tool converts interval units (Δ°C, ΔK, Δ°F, etc.) so you can work with any interval scale in heat transfer or expansion formulas.