Operative Temperature Calculator
The operative temperature a room feels like — the blend of air temperature and the radiant temperature of its surfaces — and whether it sits in the comfort band.
People feel roughly the average of the air temperature and the mean radiant temperature of the surfaces around them.
How the operative temperature calculator works
People feel roughly the average of the air temperature and the mean radiant temperature of the surfaces around them. A room at 22 °C air with a cold window wall at 14 °C feels like 18. That is why a well-insulated room feels warm at a lower thermostat setting.
At higher air speeds the air temperature counts for more; the weighting here follows the standard comfort approximation.
Formula: T_op = A × T_air + (1 − A) × T_mrt; A = 0.5 (still air), 0.6 (0.2–0.6 m/s), 0.7 (faster)
Worked examples
| Inputs | Operative temperature (°C) | Note |
|---|---|---|
| A room with a cold window wall | 20.98 | feels cooler than the thermostat |
| Well insulated | 21.57 | feels like the air temperature |
| Under a ceiling fan | 21.39 | air counts for more |
FAQFrequently asked questions
What is operative temperature?
The temperature a person actually feels — a blend of the air and the radiant temperature of surrounding surfaces. It is what comfort standards are written in.
Why does a room with big windows feel cold?
Because glass is the coldest surface in winter and you radiate heat to it. The air can be 22 °C and the room feel like 18.
What is mean radiant temperature?
The area-weighted average temperature of the surfaces you can see. Strictly it is weighted by view angle; the area average is the usual approximation.
How does insulation help comfort?
By warming the inside surfaces. A well-insulated room is comfortable at a lower air temperature, which is a real energy saving.
What comfort band should I use?
Twenty to twenty-four for winter, twenty-three to twenty-six for summer, in most standards. Adaptive standards widen it in naturally ventilated buildings.
Where these figures come from
- Sabine (1922) — Collected Papers on Acoustics — the reverberation-time equation
- CIBSE Guide A — Environmental design — daylight, comfort and ventilation criteria
- Neufert — Architects' Data — the standard reference for space and dimension
- International Code Council — International Building Code — occupant load and egress factors
- Australian Building Codes Board — National Construction Code — the body that writes Australia's building code
Last checked: September 2026. Formulas are the standard building-science and code relationships; default thresholds are common international values and should be replaced with the ones in your code.