{
    "name": "Dew Point Calculator",
    "url": "https://calculators.geekmidst.com/calculators/dew-point-calculator",
    "markdown": "https://calculators.geekmidst.com/calculators/dew-point-calculator.md",
    "category": "Everyday tools",
    "description": "Find the dew point from temperature and relative humidity, or the relative humidity from temperature and dew point, in °C or °F with the Magnus formula.",
    "summary": "The dew point is the temperature to which air must cool for its water vapour to start condensing. Unlike relative humidity, it measures how much moisture is actually in the air.",
    "also_called": [
        "Relative humidity calculator",
        "Condensation point calculator"
    ],
    "applies_to": "Worldwide",
    "last_updated": "2026-10-29",
    "computation": "Results are computed in the visitor’s browser on the HTML page. This API describes the calculator; it does not compute results.",
    "inputs": [
        {
            "name": "mode",
            "label": "Find",
            "type": "segmented",
            "default": "dew",
            "options": {
                "dew": "Dew point",
                "rh": "Relative humidity"
            }
        },
        {
            "name": "temperature",
            "label": "Air temperature",
            "type": "number",
            "default": "25"
        },
        {
            "name": "temp_unit",
            "label": "Temperature unit",
            "type": "segmented",
            "default": "c",
            "options": {
                "c": "°C",
                "f": "°F"
            }
        },
        {
            "name": "humidity",
            "label": "Relative humidity",
            "type": "number",
            "default": "60",
            "unit": "%",
            "shown_when": {
                "mode": "dew"
            }
        },
        {
            "name": "dew_point",
            "label": "Dew point",
            "type": "number",
            "default": "16.7",
            "shown_when": {
                "mode": "rh"
            }
        }
    ],
    "outputs": [
        {
            "key": "result",
            "label": "Result",
            "format": "text"
        },
        {
            "key": "dew_point_c",
            "label": "Dew point",
            "format": "number"
        },
        {
            "key": "dew_point_f",
            "label": "Dew point",
            "format": "number"
        },
        {
            "key": "humidity",
            "label": "Relative humidity",
            "format": "percent"
        },
        {
            "key": "spread_c",
            "label": "Temperature minus dew point",
            "format": "number"
        }
    ],
    "formula": {
        "text": "γ = ln(RH/100) + aT ÷ (b + T);  Td = bγ ÷ (a − γ);  RH = 100 × exp(aTd ÷ (b + Td) − aT ÷ (b + T)), with a = 17.625 and b = 243.04 °C",
        "variables": {
            "T": "air temperature in °C",
            "RH": "relative humidity in %",
            "Td": "dew point in °C",
            "a, b": "Magnus coefficients (Alduchov and Eskridge, 1996)"
        }
    },
    "worked_example": {
        "inputs": {
            "mode": "dew",
            "temperature": "25",
            "temp_unit": "c",
            "humidity": "60",
            "dew_point": "16.7"
        },
        "steps": [
            "γ = ln(0.60) + 17.625 × 25 ÷ (243.04 + 25) = −0.5108 + 1.6438 = 1.1330.",
            "Td = 243.04 × 1.1330 ÷ (17.625 − 1.1330) = 16.7 °C."
        ],
        "result": "Air at 25 °C and 60% relative humidity has a dew point of about 16.7 °C (62 °F)."
    },
    "interpretation": "Surfaces colder than the dew point get wet with condensation, which is why cold windows and pipes drip. As a rough guide, many people find dew points above about 16 °C (60 °F) muggy and above about 21 °C (70 °F) oppressive.",
    "assumptions": [
        "Over liquid water, at normal atmospheric pressure."
    ],
    "limitations": [
        "The Magnus formula is accurate to about 0.1 °C between −40 °C and 50 °C; outside that range use a more detailed equation.",
        "Below 0 °C the frost point (over ice) is slightly higher than the dew point."
    ],
    "rules": null,
    "faqs": [
        {
            "question": "Why is dew point a better measure of mugginess than humidity?",
            "answer": "Relative humidity depends on temperature: 60% at 10 °C is dry-feeling air, while 60% at 30 °C is very humid. The dew point measures the moisture itself."
        },
        {
            "question": "Can the dew point be higher than the temperature?",
            "answer": "No. When the two are equal the air is saturated (100% relative humidity) and fog or dew forms."
        }
    ],
    "sources": [],
    "related": [
        {
            "name": "Heat Index Calculator",
            "url": "https://calculators.geekmidst.com/calculators/heat-index-calculator"
        },
        {
            "name": "Wind Chill Calculator",
            "url": "https://calculators.geekmidst.com/calculators/wind-chill-calculator"
        },
        {
            "name": "Temperature Converter",
            "url": "https://calculators.geekmidst.com/calculators/temperature-converter"
        }
    ],
    "disclaimer": null,
    "publisher": "GM¹X CalcVerse"
}