What Is Room Temperature? 20 °C, 25 °C and Why It Varies
What is room temperature in Celsius? Room temperature in science is usually taken as 20 to 25 °C, which is 293 to 298 K. There is no single official value: a chemistry exam, a laboratory and a pharmacy each define it slightly differently, so the number you should use depends on the question in front of you.
What is room temperature in Celsius?
Most sources agree on a range, not one number.
| Where it is used | Value | In kelvin |
|---|---|---|
| Everyday comfort in a home | about 20 to 22 °C | 293 to 295 K |
| Typical school exam answer | 20 °C or 25 °C | 293 K or 298 K |
| SATP (standard ambient temperature and pressure) | 25 °C, 1 bar | 298 K |
| NTP (normal temperature and pressure) | 20 °C, 1 atm | 293 K |
| Pharmacy "controlled room temperature" (USP) | 20 to 25 °C | 293 to 298 K |
To change a Celsius temperature to kelvin, add 273 (or 273.15 for more precise work): 25 + 273 = 298 K.
Why does room temperature matter in chemistry?
Temperature changes how fast particles move, so it changes reaction rates, solubility and the volume of a gas. Quoting "room temperature" tells the reader the experiment was not heated or cooled, but because the value varies by a few degrees, careful work records the actual temperature from a thermometer.
What is the molar volume of a gas at room temperature?
At room temperature and pressure (RTP), 1 mole of any gas occupies about 24 dm³ (24,000 cm³). The exact figure depends on which definition of room temperature you use:
- Use the ideal gas equation, V = nRT / p.
- At 20 °C (293 K) and 1 atm (101,325 Pa): V = (1 × 8.314 × 293) / 101,325 = 0.0240 m³ = 24.0 dm³.
- At 25 °C (298 K) and 1 bar (100,000 Pa): V = (1 × 8.314 × 298) / 100,000 = 0.0248 m³ = 24.8 dm³.
Both round to about 24 to 25 dm³, which is why exam questions give you the value to use. The 0.8 dm³ difference is only about 3%, but it is enough to lose a mark if you use the wrong figure.
Does room temperature change reaction speed?
Yes. A reaction at 25 °C is faster than the same reaction at 20 °C, because the particles have more energy and more collisions are successful. As a rough rule, many reactions roughly double in speed for every 10 °C rise, though this varies between reactions. This is why a "room temperature" experiment done on a cold winter morning can give different results from one done on a warm afternoon.
Common mistakes
- Using 0 °C as "normal". Room temperature is not freezing point. Standard temperature in some data tables is 0 °C (273 K), which is a different standard from room temperature.
- Forgetting to convert to kelvin before using the gas equation. Use 293 or 298 K, never 20 or 25.
- Mixing standards. Don't take 24 dm³ (20 °C, 1 atm) and then use 25 °C in the same calculation.
Frequently asked questions
What is room temperature in Celsius?
Room temperature is 20 to 25 °C. For calculations, 25 °C is the most common choice in chemistry, and 20 °C is also widely used.
What is room temperature in kelvin?
About 293 to 298 K. Add 273 to the Celsius value: 20 °C is 293 K and 25 °C is 298 K.
Is room temperature the same as standard temperature?
No. Room temperature is about 20 to 25 °C. "Standard temperature" in some data tables is 0 °C (273 K), and "standard conditions" in thermodynamics are usually 25 °C (298 K). Always check which one your course uses.
Why is the molar volume of a gas 24 dm³ at room temperature?
Because one mole of an ideal gas at 293 K and 1 atm fills 24.0 dm³. The same gas at 273 K and 1 atm fills 22.4 dm³, which is the value for standard temperature and pressure.
Try it yourself
Open States of Matter and set the temperature to about 20 °C to see how water, ethanol and oxygen behave at room temperature: close together and sliding for the liquids, far apart and fast for the gas. Then drag the heater up or down and watch the particles speed up or slow down. To see how pressure and temperature change a gas's volume, try Gas Laws.
See it for yourself, in 3D and free.
Try it in the States of Matter