{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"relative-humidity"},"result":{"entity_type":"calculator","id":"relative-humidity","calculator_id":"relative-humidity","canonical_url":"https://tttkmbb.com/weather/relative-humidity","name":"Relative Humidity Calculator","title":"Relative Humidity Calculator – RH and Absolute Humidity from Temperature and Dew Point","category":"weather","category_name":"Weather & Environment","tool_name":"calculate_relative_humidity","featured_mcp_tool":false,"description":"Computes relative humidity from air temperature and dew point as the ratio of Magnus-formula vapour pressures, and the absolute humidity (grams of water vapour per cubic metre) from the ideal-gas law for water vapour.","use_when":"A weather report gives temperature and dew point and you need the relative humidity, or you need the water-vapour content of air in g/m³ (e.g. for drying, greenhouses or HVAC).","do_not_use_when":"You have relative humidity and need the dew point (use dew-point), or you need humidity ratio in g/kg of dry air, which also requires the air pressure.","inputs":[{"name":"temperature","label":"Air temperature","type":"number","required":true,"min":-60,"max":140,"description":"Air (dry-bulb) temperature in temperature_unit.","example":25},{"name":"dew_point","label":"Dew point","type":"number","required":true,"min":-80,"max":140,"description":"Dew point temperature in temperature_unit; cannot exceed the air temperature.","example":19.15},{"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"}],"outputs":[{"name":"relative_humidity_percent","label":"Relative humidity","type":"number","unit":"%","decimals":1,"description":"RH = 100 × es(Td) / es(T)."},{"name":"absolute_humidity_g_m3","label":"Absolute humidity","type":"number","unit":"g/m³","decimals":2,"description":"Mass of water vapour per cubic metre of air, e / (Rv × T_K)."},{"name":"vapor_pressure_hpa","label":"Actual vapour pressure","type":"number","unit":"hPa","decimals":2,"description":"Partial pressure of water vapour, es(Td)."},{"name":"saturation_vapor_pressure_hpa","label":"Saturation vapour pressure","type":"number","unit":"hPa","decimals":2,"description":"es(T) at the air temperature."},{"name":"saturation_absolute_humidity_g_m3","label":"Saturation absolute humidity","type":"number","unit":"g/m³","decimals":2,"description":"Water vapour content the air could hold at 100 % RH and this temperature."},{"name":"dew_point_depression_c","label":"Dew point depression","type":"number","unit":"°C","decimals":1,"description":"T − Td in Celsius."},{"name":"comfort","label":"Comfort level","type":"string","decimals":4,"description":"NWS dew-point comfort band."}],"input_schema":{"type":"object","properties":{"temperature":{"description":"Air (dry-bulb) temperature in temperature_unit.","type":"number","minimum":-60,"maximum":140,"examples":[25]},"dew_point":{"description":"Dew point temperature in temperature_unit; cannot exceed the air temperature.","type":"number","minimum":-80,"maximum":140,"examples":[19.15]},"temperature_unit":{"description":"Unit of the temperature input(s).","type":"string","enum":["c","f"],"default":"c","examples":["c"]}},"additionalProperties":false,"required":["temperature","dew_point"]},"output_schema":{"type":"object","properties":{"relative_humidity_percent":{"description":"RH = 100 × es(Td) / es(T). Unit: %.","type":"number","x-unit":"%"},"absolute_humidity_g_m3":{"description":"Mass of water vapour per cubic metre of air, e / (Rv × T_K). Unit: g/m³.","type":"number","x-unit":"g/m³"},"vapor_pressure_hpa":{"description":"Partial pressure of water vapour, es(Td). Unit: hPa.","type":"number","x-unit":"hPa"},"saturation_vapor_pressure_hpa":{"description":"es(T) at the air temperature. Unit: hPa.","type":"number","x-unit":"hPa"},"saturation_absolute_humidity_g_m3":{"description":"Water vapour content the air could hold at 100 % RH and this temperature. Unit: g/m³.","type":"number","x-unit":"g/m³"},"dew_point_depression_c":{"description":"T − Td in Celsius. Unit: °C.","type":"number","x-unit":"°C"},"comfort":{"description":"NWS dew-point comfort band.","type":"string"}}},"formula":"es(T) = 6.1094·exp(17.625·T/(243.04 + T)) hPa (T in °C); RH = 100·es(Td)/es(T); absolute humidity = 100·es(Td) / (461.5 · (T + 273.15)) kg/m³ × 1000","method":"Magnus formula with Alduchov & Eskridge (1996) coefficients; water vapour treated as an ideal gas with Rv = 461.5 J/(kg·K). Accurate to about 0.5 % RH for −40 to +50 °C.","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"}],"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, dew point 19.15 °C","inputs":{"temperature":25,"dew_point":19.15,"temperature_unit":"c"},"expected":{"relative_humidity_percent":70,"absolute_humidity_g_m3":16.09,"vapor_pressure_hpa":22.13,"saturation_vapor_pressure_hpa":31.62,"dew_point_depression_c":5.9},"url":"https://tttkmbb.com/api/v1/calculate/relative-humidity?temperature=25&dew_point=19.15&temperature_unit=c"},{"name":"30 °C, dew point 10 °C","inputs":{"temperature":30,"dew_point":10,"temperature_unit":"c"},"expected":{"relative_humidity_percent":28.9,"absolute_humidity_g_m3":8.76,"saturation_absolute_humidity_g_m3":30.28},"url":"https://tttkmbb.com/api/v1/calculate/relative-humidity?temperature=30&dew_point=10&temperature_unit=c"}],"faq":[{"q":"Can relative humidity exceed 100 %?","a":"Not in this calculator: a dew point above the air temperature is physically impossible for saturated equilibrium and returns an error."},{"q":"What is the difference between absolute humidity and humidity ratio?","a":"Absolute humidity is grams of vapour per cubic metre of moist air; the humidity ratio (mixing ratio) is grams of vapour per kilogram of dry air and needs the total air pressure."}],"tags":["relative humidity","absolute humidity","dew point to humidity","vapor pressure","g/m3 water vapour"],"related":[{"calculator_id":"dew-point","reason":"Inverse: dew point from temperature and relative humidity."},{"calculator_id":"air-density","reason":"Density of moist air from temperature, pressure and humidity."},{"calculator_id":"heat-index","reason":"Apparent temperature from temperature and humidity."}],"links":{"html":"https://tttkmbb.com/weather/relative-humidity","markdown":"https://tttkmbb.com/weather/relative-humidity.md","json":"https://tttkmbb.com/weather/relative-humidity.json","api":"https://tttkmbb.com/api/v1/calculate/relative-humidity","schema":"https://tttkmbb.com/api/v1/calculators/relative-humidity","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-24"},"timestamp":"2026-09-24T01:49:42Z","next_actions":[{"tool":"run_calculator","calculator_id":"relative-humidity","reason":"Run Relative Humidity Calculator with the inputs above."}],"links":{"markdown":"https://tttkmbb.com/weather/relative-humidity.md"}}