Humidity Calculator

This calculator uses the Magnus formula to find saturation vapor pressure. The equation is: SVP = 6.112 × e^(17.67 × T / (T + 243.5)), where T is the temperature in °C. This is the same formula used by weather services and meteorologists around the world. It is accurate for temperatures between −90°C and 60°C.

The three values — air temperature, dew point, and relative humidity — are all linked by a single equation. If you know any two, the math can solve for the third. Leaving one field blank tells the calculator which value you want it to find. If you fill in all three or only one, the calculator cannot work.

A psychrometer is a tool with two thermometers side by side. One has a dry bulb that reads the regular air temperature. The other has a wet bulb wrapped in a damp cloth. The difference between the two readings tells you how much moisture is in the air. This calculator's wet-bulb/dry-bulb method uses those two readings to find relative humidity.

The wet bulb cools down because water evaporates from the cloth around it. Evaporation always takes heat away, so the wet-bulb reading must be the same as or lower than the dry-bulb reading. If it were higher, it would mean evaporation is adding heat, which does not happen in normal conditions.

No. The dew point can equal the air temperature at most, which means the air is fully saturated at 100% relative humidity. It cannot go above the air temperature. If you enter a dew point higher than the air temperature, the calculator will show an error.

The chart plots saturation vapor pressure against temperature. It shows a curved line that rises steeply as temperature goes up. Two dots are marked on the chart — a red dot for the air temperature and a green dot for the dew point. The gap between them shows how far the air is from being fully saturated.

The Magnus formula used here is accurate to within about ±0.4% for temperatures between −40°C and 50°C. For extreme temperatures outside the range of −90°C to 60°C, the calculator will show a warning because results may be less reliable.

Most experts recommend keeping indoor humidity between 30% and 50%. Below 30%, the air feels dry and can cause dry skin, nosebleeds, and static electricity. Above 50%, moisture can build up on windows and walls, which encourages mold and dust mites.

You can use a digital hygrometer or a home weather station. Many of these devices show air temperature, relative humidity, and dew point all at once. If you have any two of those values, you can enter them into this calculator to find the third or to see the full step-by-step solution.

It supports °F (Fahrenheit) and °C (Celsius). You can switch between them at any time using the unit toggle buttons. When you switch, the calculator automatically converts the values you already entered so you do not need to re-type them.

Your body cools itself by sweating. When humidity is high, sweat does not evaporate as fast, so you feel hotter. On a cooler day with the same humidity percentage, your body does not need to cool down as much, so the moisture in the air bothers you less.

Absolute humidity is the actual mass of water vapor in a given volume of air, measured in grams per cubic meter (g/m³). Unlike relative humidity, it does not change with temperature. This calculator uses absolute humidity to compute the humidity deficit shown in the results.

Humidity deficit tells you how much more moisture the air can absorb. A high deficit means water evaporates quickly from soil and plant leaves, so plants may need more watering. A low deficit means the air is nearly full of moisture, and plants lose less water. Greenhouse growers watch this number closely to keep plants healthy.

Yes. HVAC technicians often need to find dew point and relative humidity to size dehumidifiers, set thermostat targets, and prevent condensation on ducts and windows. Enter your indoor temperature and one other known value, and the calculator gives you everything you need, including step-by-step math you can include in reports.

The comfort rating is a plain-language label based on the relative humidity result. It ranges from Very Dry (below 25%) to Very Humid (above 70%). It gives you a quick idea of how the air would feel to most people without needing to interpret the numbers yourself.

The dew point method uses only temperature and is not affected by altitude. The wet-bulb/dry-bulb method in this calculator uses standard sea-level pressure (1013.25 hPa) for the psychrometric correction. If you are at a very high altitude, the wet-bulb result may be slightly less accurate, but for most locations the difference is small.

If the air temperature and dew point are equal, or if the dry-bulb and wet-bulb temperatures are equal, the relative humidity is 100%. This means the air is fully saturated and cannot hold any more water vapor. Fog, dew, or condensation is likely at this point.