WMO-No. 8 humidity equations
Dew Point over Water
Calculate thermodynamic dew-point temperature from dry-bulb temperature and relative humidity with respect to water. The WMO water and ice formula ranges are enforced—no extrapolated result is shown.
WMO-range result
WMO-No. 8, Guide to Instruments and Methods of Observation, Volume I, Chapter 4, Annex 4.B gives ew(t)=6.112 exp[17.62t/(243.12+t)] for water from −45 to 60°C and ei(t)=6.112 exp[22.46t/(272.62+t)] for ice from −65 to 0°C. WMO e-Library chapter viewer.
The WMO International Cloud Atlas glossary defines dew point with respect to a water surface and relative humidity as observed vapour pressure divided by saturation vapour pressure at the same temperature and pressure.
Corrections to the former calculator: t−td is dew-point depression, not wet-bulb depression. Wet-bulb temperature is a separate pressure-dependent psychrometric quantity. The former vapour-pressure result mixed a second coefficient set and omitted the moist-air enhancement factor, so it has been removed. Comfort bands, presets and unsourced FAQ claims were also removed.
Nikolai Shelkovenko
Nikolai Shelkovenko is a vibration analysis engineer and the founder and CEO of Vibromera. For more than 15 years he has balanced rotating equipment in the field rather than on a test bench: mulchers, industrial fans, crushers, centrifuges, shafts and spindles. That work is what the Balanset instruments grew out of — they were designed as a tool a specialist can carry to the machine and use alone, on site, not as laboratory equipment. Vibromera was founded in 2017 and has been based in Porto, Portugal, since 2023. Development, assembly and support of the Balanset line all happen here. The flagship instrument is the Balanset-1A, a portable analyser for single- and two-plane balancing and for vibration diagnostics. Nikolai is personally involved in customer support, in working through difficult balancing cases and in the development of the software. He works with customers worldwide, in any language.
