Humidity Calculator
Calculate relative, absolute humidity, and dew point for home, cooking, or plant care
Humidity Results
How to Use This Tool
Follow these simple steps to get accurate humidity readings for your home, kitchen, or garden:
- Select your calculation type: choose whether you have wet bulb temperature (measured with a hygrometer) or dew point temperature (often provided in weather reports).
- Enter your dry bulb (air) temperature, then input your wet bulb or dew point temperature in the same unit (Celsius or Fahrenheit).
- Adjust the temperature unit dropdown to match your measurement system.
- Optionally enter local atmospheric pressure (defaults to standard sea-level pressure if left blank).
- Click the Calculate Humidity button to see detailed results, or Reset to clear all fields.
- Use the Copy Results button to save your readings for cooking, plant care, or home adjustments.
Formula and Logic
This calculator uses the Magnus-Tetens approximation, a widely accepted formula for humidity calculations in everyday conditions:
- Saturation Vapor Pressure: Calculated as 6.112 * exp( (17.67 * T) / (T + 243.5) ), where T is temperature in Celsius. This represents the maximum water vapor air can hold at a given temperature.
- Dew Point: Derived from vapor pressure using Td = (243.5 * ln(e/6.112)) / (17.67 - ln(e/6.112)), where e is actual vapor pressure.
- Relative Humidity: (Actual Vapor Pressure / Saturation Vapor Pressure) * 100%, representing how full the air is with water vapor.
- Absolute Humidity: 216.7 * (e / (T + 273.15)), measured in grams of water per cubic meter of air.
All temperature inputs are converted to Celsius for calculation, then converted back to your selected unit for display.
Practical Notes
These lifestyle-specific tips help you apply humidity readings to daily decisions:
- For home baking: Ideal humidity for bread proofing is 70-80% RH; adjust oven humidity by placing a water pan inside if your kitchen is dry.
- For houseplants: Tropical plants thrive at 60-80% RH, while succulents prefer 30-50% RH. Use a humidifier or pebble tray if readings are too low.
- For home comfort: Keep indoor RH between 30-60% to avoid dry skin, static electricity, or mold growth. Use a dehumidifier if RH exceeds 60%.
- For outdoor planning: Dew point above 18°C (64°F) feels muggy; dew point below 10°C (50°F) feels dry. Check readings before exercising or gardening.
- Wet bulb temperature can be measured by wrapping a thermometer in a damp cloth and fanning it until the temperature stabilizes.
Why This Tool Is Useful
Most weather apps only report relative humidity, which can be misleading without context. This tool gives you actionable data:
- Home cooks can adjust recipes for high-humidity days (e.g., reduce liquid in dough when RH is above 70%).
- Homeowners can prevent mold growth by monitoring basement or bathroom humidity levels.
- Plant owners can tailor care routines to match their indoor humidity conditions.
- Daily planners can check dew points to decide if outdoor activities will feel comfortable.
Frequently Asked Questions
What is a normal indoor humidity level?
For most homes, indoor relative humidity between 30% and 60% is ideal. Levels below 30% can cause dry skin, irritated eyes, and static electricity. Levels above 60% increase the risk of mold, dust mites, and musty odors.
How do I measure wet bulb temperature at home?
Wrap a standard thermometer in a damp paper towel, then fan it continuously for 1-2 minutes until the temperature stops dropping. The stabilized reading is your wet bulb temperature. Ensure the cloth is damp but not dripping.
Why does relative humidity change with temperature?
Warm air can hold more water vapor than cool air. If air temperature rises without adding moisture, relative humidity drops. If temperature drops (e.g., overnight), relative humidity rises, which is why dew forms when dew point equals air temperature.
Additional Guidance
Use these tips to get the most accurate results from this calculator:
- Measure air temperature in the shade, away from direct sunlight or heat sources (e.g., ovens, radiators) for accurate readings.
- If you don't have a hygrometer, check local weather reports for dew point or relative humidity data to input into the tool.
- For high-altitude locations, adjust atmospheric pressure to match your local elevation (pressure drops ~1 hPa per 8 meters of elevation gain).
- Re-calculate humidity if temperature changes significantly (e.g., moving from a cool basement to a warm kitchen) for accurate results.