{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"dew-point"},"result":{"entity_type":"calculator","id":"dew-point","calculator_id":"dew-point","canonical_url":"https://tttkmbb.com/weather/dew-point","name":"Dew Point Calculator","title":"Dew Point Calculator – Dew Point from Temperature and Relative Humidity (Magnus Formula)","category":"weather","category_name":"Weather & Environment","tool_name":"calculate_dew_point","featured_mcp_tool":false,"description":"Computes the dew point temperature from air temperature and relative humidity with the Magnus formula (Alduchov & Eskridge coefficients a = 17.625, b = 243.04 °C), plus vapour pressures and a comfort classification.","use_when":"You know temperature and relative humidity and need the dew point, the humidity comfort level, or the temperature at which condensation forms on a surface.","do_not_use_when":"You know the dew point and need relative humidity or absolute humidity (use relative-humidity), or the temperature is below −40 °C or above 50 °C where the Magnus fit is not validated.","inputs":[{"name":"temperature","label":"Air temperature","type":"number","required":true,"min":-60,"max":140,"description":"Air (dry-bulb) temperature in temperature_unit; the fit is validated for −40 to +50 °C.","example":25},{"name":"temperature_unit","label":"Temperature unit","type":"enum","required":false,"default":"c","values":[{"value":"c","label":"Celsius (°C)","aliases":["celsius","°c","degc"]},{"value":"f","label":"Fahrenheit (°F)","aliases":["fahrenheit","°f","degf"]}],"description":"Unit of the temperature input(s).","example":"c"},{"name":"relative_humidity_percent","label":"Relative humidity","type":"number","unit":"%","required":true,"min":1,"max":100,"description":"Relative humidity in percent (70 means 70 %).","example":70}],"outputs":[{"name":"dew_point_c","label":"Dew point","type":"number","unit":"°C","decimals":1,"description":"Temperature at which the air would be saturated (100 % RH) at constant pressure."},{"name":"dew_point_f","label":"Dew point","type":"number","unit":"°F","decimals":1,"description":"Dew point in Fahrenheit."},{"name":"dew_point_depression_c","label":"Dew point depression","type":"number","unit":"°C","decimals":1,"description":"Air temperature minus dew point; 0 means saturated air (fog or dew likely)."},{"name":"vapor_pressure_hpa","label":"Actual vapour pressure","type":"number","unit":"hPa","decimals":2,"description":"Partial pressure of water vapour, e = RH/100 × es(T)."},{"name":"saturation_vapor_pressure_hpa","label":"Saturation vapour pressure","type":"number","unit":"hPa","decimals":2,"description":"es(T) over liquid water from the Magnus formula."},{"name":"comfort","label":"Comfort level","type":"string","decimals":4,"description":"NWS comfort bands: below 55 °F dry, 55–65 °F sticky, 65 °F and above oppressive."}],"input_schema":{"type":"object","properties":{"temperature":{"description":"Air (dry-bulb) temperature in temperature_unit; the fit is validated for −40 to +50 °C.","type":"number","minimum":-60,"maximum":140,"examples":[25]},"temperature_unit":{"description":"Unit of the temperature input(s).","type":"string","enum":["c","f"],"default":"c","examples":["c"]},"relative_humidity_percent":{"description":"Relative humidity in percent (70 means 70 %). Unit: %.","type":"number","minimum":1,"maximum":100,"examples":[70],"x-unit":"%"}},"additionalProperties":false,"required":["temperature","relative_humidity_percent"]},"output_schema":{"type":"object","properties":{"dew_point_c":{"description":"Temperature at which the air would be saturated (100 % RH) at constant pressure. Unit: °C.","type":"number","x-unit":"°C"},"dew_point_f":{"description":"Dew point in Fahrenheit. Unit: °F.","type":"number","x-unit":"°F"},"dew_point_depression_c":{"description":"Air temperature minus dew point; 0 means saturated air (fog or dew likely). Unit: °C.","type":"number","x-unit":"°C"},"vapor_pressure_hpa":{"description":"Partial pressure of water vapour, e = RH/100 × es(T). Unit: hPa.","type":"number","x-unit":"hPa"},"saturation_vapor_pressure_hpa":{"description":"es(T) over liquid water from the Magnus formula. Unit: hPa.","type":"number","x-unit":"hPa"},"comfort":{"description":"NWS comfort bands: below 55 °F dry, 55–65 °F sticky, 65 °F and above oppressive.","type":"string"}}},"formula":"γ = ln(RH/100) + a·T/(b + T); Td = b·γ/(a − γ) with a = 17.625, b = 243.04 °C, T in °C; es(T) = 6.1094·exp(a·T/(b + T)) hPa; e = RH/100 · es(T)","method":"Magnus-type formula with the Alduchov & Eskridge (1996) coefficients, accurate to about ±0.35 °C for −40 to +50 °C over liquid water. The dew point does not depend on air pressure as long as the vapour content is unchanged.","sources":[{"name":"Alduchov OA, Eskridge RE (1996) Improved Magnus form approximation of saturation vapor pressure, J Appl Meteorol 35:601-609","url":"https://journals.ametsoc.org/view/journals/apme/35/4/1520-0450_1996_035_0601_imfaos_2_0_co_2.xml","type":"peer_reviewed","retrieved_at":"2026-09-24"},{"name":"Wikipedia – Dew point","url":"https://en.wikipedia.org/wiki/Dew_point","type":"reference","retrieved_at":"2026-09-24"},{"name":"NWS La Crosse – Dew point vs humidity (comfort thresholds)","url":"https://www.weather.gov/arx/why_dewpoint_vs_humidity","type":"government","retrieved_at":"2026-09-24"}],"freshness":{"type":"static","max_age_seconds":null,"note":"Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output."},"examples":[{"name":"25 °C, 70 % RH","inputs":{"temperature":25,"temperature_unit":"c","relative_humidity_percent":70},"expected":{"dew_point_c":19.1,"dew_point_f":66.5,"dew_point_depression_c":5.9,"vapor_pressure_hpa":22.13,"saturation_vapor_pressure_hpa":31.62,"comfort":"Oppressive: air heavy with moisture, uncomfortable for most people (65 °F / 18 °C and above)"},"url":"https://tttkmbb.com/api/v1/calculate/dew-point?temperature=25&temperature_unit=c&relative_humidity_percent=70"},{"name":"86 °F, 40 % RH","inputs":{"temperature":86,"temperature_unit":"f","relative_humidity_percent":40},"expected":{"dew_point_c":14.9,"dew_point_f":58.9,"comfort":"Sticky: noticeably humid, muggy evenings (55–65 °F / 13–18 °C)"},"url":"https://tttkmbb.com/api/v1/calculate/dew-point?temperature=86&temperature_unit=f&relative_humidity_percent=40"}],"faq":[{"q":"Dew point or relative humidity: which describes mugginess?","a":"Dew point. Relative humidity depends on temperature (90 % RH at 5 °C is dry air), whereas a dew point above about 18 °C (65 °F) feels oppressive at any temperature."},{"q":"What if the dew point is below 0 °C?","a":"Below 0 °C the frost point (saturation over ice) would differ slightly; this calculator always uses the over-water Magnus formula, as most meteorological reports do."}],"tags":["dew point","dew point calculator","humidity comfort","magnus formula","condensation temperature"],"related":[{"calculator_id":"relative-humidity","reason":"Inverse problem: relative and absolute humidity from temperature and dew point."},{"calculator_id":"heat-index","reason":"Apparent temperature from temperature and humidity."},{"calculator_id":"air-density","reason":"Humidity also lowers air density."}],"links":{"html":"https://tttkmbb.com/weather/dew-point","markdown":"https://tttkmbb.com/weather/dew-point.md","json":"https://tttkmbb.com/weather/dew-point.json","api":"https://tttkmbb.com/api/v1/calculate/dew-point","schema":"https://tttkmbb.com/api/v1/calculators/dew-point","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-24"},"timestamp":"2026-09-24T01:45:40Z"}