DEW POINT CALCULATOR by WeatherStationAdvisor
Units:
Temperature (T)
Relative Humidity (RH)
Dew Point (DP)
68 °F
= 20.0°C
120°F
−40°F
50 %
 
100%
1%
49 °F
= 9.4°C
100°F
−40°F
Preservation metrics
Preservation Index: estimated lifespan of archival materials (paper, photos, film). Above 75 years is good. Below 45 is risky for irreplaceable materials.
Natural aging (PI)
44 yrs
RISK
Mold spores activate when RH stays above 65–70% for extended periods. Keeping RH below 60% essentially eliminates mold risk.
Mold risk
Low
GOOD
Equilibrium Moisture Content: moisture absorbed by wood and paper. High EMC causes warping and mechanical damage. Target range is 7–12%.
% EMC
9.3%
OK
RH above 60% accelerates oxidation of metals. Critical for instruments, coins, electronics, and archival metals.
Metal corrosion
Low
OK
DryComfortableMuggyOppressive
Comfortable Outdoor activity is comfortable with no humidity concerns.
The difference between air temperature and dew point. When this drops to 4°F (2°C) or less, fog or low clouds are likely. Pilots check this before every flight.
T / DP spread
19°F
No fog risk
The actual mass of water vapor in the air, in grams per cubic metre. Unlike relative humidity, this value doesn't change as temperature rises and falls.
Abs. humidity
8.6 g/m³
Water vapor mass
Frost can form on exposed surfaces when the dew point is at or below 32°F (0°C), even if the air temperature stays above freezing. Surface temps can drop several degrees below air temp on calm, clear nights.
Frost risk
None
DP above 36°F
Fog forms when the T/DP spread collapses to 4°F (2°C) or less, meaning air is nearly saturated. A spread of 1°F or less usually means fog is already present or imminent.
Fog risk
Low
Spread > 4°F
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