Temperature Conversion Calculator
Enter a temperature in any scale to get the other two exactly, with the absolute-zero guard and the ΔT conversion rule HVAC calculations actually use.
Last updated: 2026-09-28
How the calculation works
- Absolute conversions use the exact definitions — no rounded constants.
- Input below absolute zero is rejected rather than producing a negative-Kelvin nonsense result.
- The notes carry the HVAC-critical rule: temperature DIFFERENCES convert with ×1.8 only, never +32.
Formula
°F = °C × 1.8 + 32 K = °C + 273.15 ΔT: °F difference = °C difference × 1.8 (no +32)
| Symbol | Meaning | Unit |
|---|---|---|
T | Temperature | °C / °F / K |
ΔT | Temperature difference | °C or K ↔ °F × 1.8 |
Worked example
20 °C = 68 °F = 293.15 K. A 20 °F design ΔT is 11.1 °C — not 52 °F! The ΔT trap is the most common conversion error in HVAC math translated between unit systems.
Interpreting the result
The single most common mistake is applying +32 to a temperature difference: a '9 °F split' across a coil is 5 °C, not −12.8 °C. Load formulas (Q = 1.08 × CFM × ΔT) and U-factor math all take ΔT in consistent units — convert the difference with ×1.8, then apply. International equipment specs in °C convert to US practice and back this way without error.
Assumptions
- Exact scale definitions; no approximation.
- Deliberately simple — for weather-feel metrics use the dew point, heat index and wind chill calculators.
Limitations
- Temperature conversion only — it cannot substitute for psychrometric or comfort calculations.
Frequently asked questions
How do I convert Celsius to Fahrenheit?
Multiply by 1.8 and add 32: 20 °C → 20 × 1.8 + 32 = 68 °F. For temperature differences, multiply by 1.8 only.
What is absolute zero in Fahrenheit?
−459.67 °F (0 K, −273.15 °C). The calculator rejects inputs below it instead of returning unphysical results.