Room Temperature Calculator

Enter (or auto-detect) the outdoor temperature, then tell the calculator whether your windows are open, whether AC or heating is running (and at what set temperature and for how long), and your approximate room size. It combines these into a single estimate.

Outdoor temperature alone only gives a rough starting point. Windows, AC or heating use and their set temperature, and room size all shift the indoor temperature meaningfully away from the outdoor reading.

Yes. Open windows move indoor temperature much closer to outdoor temperature and reduce how effective AC or heating can be.

It depends on the set temperature you choose, how long it has run, and the room size. With windows closed, the room will move toward your AC's set temperature but typically settle a little above it, since outdoor heat keeps working against the AC.

Usually not exactly. The set temperature strongly pulls the estimate, but outdoor conditions, open windows, and the simplified nature of the model mean the room typically settles close to — rather than precisely at — the setpoint.

Most of the change happens within the first one to two hours, with smaller further gains after that as the room approaches its cooling equilibrium. Smaller rooms cool faster than larger ones.

Yes. Smaller rooms have less air to condition and respond faster to AC or heating than larger rooms, given the same running time — though the size of the room doesn't change the equilibrium it's heading toward.

A running heater gradually pulls the room toward its set temperature. Effectiveness builds with running time and is reduced if windows are open.

Only a little on its own — it mainly moves air around rather than cooling or heating it. Its biggest effect is helping AC or heating reach their equilibrium faster by improving air circulation.

No. This calculator estimates indoor temperature — it does not measure the actual air temperature. For an exact reading, use an indoor thermometer.

There's no single formula, because indoor temperature depends on several things at once. This calculator starts from the outdoor temperature and estimates how far windows, room size, AC or heater use, and a fan move the room toward its likely temperature over time. Enter those details above to get an estimate.

This calculator can't read your room's actual temperature, because it has no sensor in your room. It gives an estimate from the outdoor temperature, your windows, AC or heater use, fan, and room size. For the exact current temperature, use an indoor thermometer.

You can get a rough idea with the estimator above, which uses outdoor weather and how your room is being heated or cooled. It is an estimate, not a measurement. Some phone apps claim to show room temperature, but many phones have no dedicated room-temperature sensor, so those readings are often estimates too. For more methods and practical tips, read our complete guide to checking room temperature without a thermometer.

A website can only estimate your room temperature unless it is connected to a sensor in your room. This calculator is an online estimator: it works from the details you enter and the outdoor temperature, not from a live reading of your room.