Use a thermometer to measure the air in the room
Place the thermometer away from direct sunlight, heaters, vents, and appliances
Wait a few minutes for the reading to stabilize
Read the temperature shown on the thermometer
Check a digital thermostat if the room has one
Use a weather app or indoor sensor only if it measures indoor temperature
Compare the reading to the typical room temperature range if needed
Repeat the measurement in a few spots for a more accurate average