Humidity & Dew Point Calculator

ANA›Life Services Authority›National Calculator Authority›Humidity & Dew Point Calculator

.calc-container { max-width: 640px; margin: 2rem 0; padding: 1.5rem; background: #fff; border: 1px solid #ddd; border-radius: 8px; box-shadow: 0 1px 3px rgba(0,0,0,0.06); font-family: system-ui, -apple-system, sans-serif; } .calc-container h3 { font-family: Georgia, serif; font-size: 1.15rem; color: #1a1a1a; margin-bottom: 1rem; padding-bottom: 0.5rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-row { display: flex; align-items: center; gap: 0.75rem; margin-bottom: 0.75rem; flex-wrap: wrap; } .calc-row label { min-width: 160px; font-size: 0.9rem; color: #333; font-weight: 500; } .calc-row input[type="number"], .calc-row select { flex: 1; min-width: 120px; max-width: 200px; padding: 0.5rem 0.6rem; border: 1px solid #ccc; border-radius: 4px; font-size: 0.9rem; font-family: system-ui, sans-serif; color: #1a1a1a; background: #fafaf8; } .calc-row input:focus, .calc-row select:focus { outline: none; border-color: var(--ac, #3d5a80); box-shadow: 0 0 0 2px rgba(26,74,138,0.12); } .calc-row .unit { font-size: 0.82rem; color: #888; min-width: 30px; } .calc-btn { display: inline-block; margin-top: 0.5rem; padding: 0.55rem 1.5rem; background: var(--ac, #3d5a80); color: #fff; border: none; border-radius: 4px; font-size: 0.9rem; font-weight: 600; cursor: pointer; font-family: system-ui, sans-serif; } .calc-btn:hover { opacity: 0.9; } .calc-result { margin-top: 1.25rem; padding: 1rem 1.25rem; background: #f0f6fc; border-left: 3px solid var(--ac, #3d5a80); border-radius: 0 6px 6px 0; display: none; } .calc-result.visible { display: block; } .calc-result-label { font-size: 0.78rem; text-transform: uppercase; letter-spacing: 0.06em; color: #666; margin-bottom: 0.25rem; } .calc-result-value { font-size: 1.6rem; font-weight: 700; color: var(--ac, #3d5a80); } .calc-result-detail { font-size: 0.85rem; color: #555; margin-top: 0.5rem; line-height: 1.5; } .calc-note { margin-top: 1rem; font-size: 0.8rem; color: #888; font-style: italic; } .calc-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 0.75rem; margin-top: 0.75rem; } .calc-grid-item { padding: 0.6rem 0.8rem; background: #f8f9fa; border-radius: 4px; border: 1px solid #eee; } .calc-grid-item .label { font-size: 0.75rem; color: #888; text-transform: uppercase; letter-spacing: 0.04em; } .calc-grid-item .value { font-size: 1.1rem; font-weight: 600; color: #1a1a1a; } @media (max-width: 720px) { .calc-row { flex-direction: column; align-items: flex-start; gap: 0.3rem; } .calc-row label { min-width: auto; } .calc-row input[type="number"], .calc-row select { max-width: 100%; width: 100%; } .calc-grid { grid-template-columns: 1fr; } } .calc-chart { margin: 1rem 0; text-align: center; } .calc-chart svg { max-width: 100%; height: auto; } .calc-chart-legend { display: flex; flex-wrap: wrap; justify-content: center; gap: 0.6rem 1.2rem; margin-top: 0.6rem; font-size: 0.8rem; color: #555; } .calc-chart-legend span { display: inline-flex; align-items: center; gap: 0.3rem; } .calc-chart-legend i { display: inline-block; width: 10px; height: 10px; border-radius: 2px; font-style: normal; } .calc-related { max-width: 640px; margin: 2rem 0 1rem; padding: 1.25rem 1.5rem; background: #f8f9fa; border: 1px solid #e8e8e8; border-radius: 8px; } .calc-related h3 { font-family: Georgia, serif; font-size: 1rem; color: #1a1a1a; margin: 0 0 0.75rem; padding-bottom: 0.4rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-related-list { list-style: none; padding: 0; margin: 0 0 0.75rem; display: grid; grid-template-columns: 1fr 1fr; gap: 0.4rem 1.5rem; } .calc-related-list li a { font-size: 0.88rem; color: var(--ac, #3d5a80); text-decoration: none; } .calc-related-list li a:hover { text-decoration: underline; } .calc-browse-all { margin: 0.5rem 0 0; font-size: 0.9rem; font-weight: 600; } .calc-browse-all a { color: var(--ac, #3d5a80); text-decoration: none; } .calc-browse-all a:hover { text-decoration: underline; } @media (max-width: 720px) { .calc-related-list { grid-template-columns: 1fr; } }

Humidity & Dew Point Calculator

Calculate dew point temperature, absolute humidity, wet-bulb temperature, and vapor pressure from air temperature and relative humidity using the Magnus formula and psychrometric equations.

Air Temperature

°C °F K

Relative Humidity (%)

Atmospheric Pressure (hPa) (optional)

Output Temperature Unit

°C °F K

Calculate

### Results

(function() {

/ ── helpers ── / function toC(val, unit) { if (unit === "C") return val; if (unit === "F") return (val - 32) * 5 / 9; if (unit === "K") return val - 273.15; } function fromC(val, unit) { if (unit === "C") return val; if (unit === "F") return val * 9 / 5 + 32; if (unit === "K") return val + 273.15; } function fmt(v, d) { return isFinite(v) ? v.toFixed(d) : "—"; } function unitLabel(u) { return u === "C" ? "°C" : u === "F" ? "°F" : "K"; }

/ ── Magnus / Buck constants (August-Roche-Magnus) ── / // Valid range: -40 °C to 60 °C const A = 17.625; // dimensionless const B = 243.04; // °C

/ Saturation vapor pressure (hPa) via Buck equation / function esat(T_C) { return 6.1078 * Math.exp((A * T_C) / (B + T_C)); }

/ Dew point (°C) — Magnus inversion / function dewPoint(T_C, RH) { const gamma = Math.log(RH / 100) + (A * T_C) / (B + T_C); return (B * gamma) / (A - gamma); }

/ Absolute humidity (g/m³) / // AH = (RH/100) * 6.112 * exp(17.67*T/(T+243.5)) * 2165 / (T+273.15) // Simplified: AH = (e_actual * Mw) / (Rv * T_K) // Using: AH [g/m³] = 216.7 * e_actual [hPa] / T_K function absoluteHumidity(T_C, RH) { const e_actual = (RH / 100) * esat(T_C); const T_K = T_C + 273.15; return 216.7 * e_actual / T_K; }

/ Wet-bulb temperature (°C) — Stull (2011) empirical formula / // Tw = Tatan(0.151977(RH+8.313659)^0.5) + atan(T+RH) // - atan(RH-1.676331) + 0.00391838RH^1.5atan(0.023101*RH) - 4.686035 function wetBulb(T_C, RH) { const r = RH; return T_C * Math.atan(0.151977 * Math.pow(r + 8.313659, 0.5)) + Math.atan(T_C + r) - Math.atan(r - 1.676331) + 0.00391838 * Math.pow(r, 1.5) * Math.atan(0.023101 * r) - 4.686035; }

/ Specific humidity (g/kg) / function specificHumidity(T_C, RH, P_hPa) { const e = (RH / 100) * esat(T_C); return 621.97 * e / (P_hPa - 0.378 * e); }

/ Humidex (Canada) — feels-like index / function humidex(T_C, Td_C) { const e = esat(Td_C); return T_C + 0.5555 * (e - 10.0); }

/ ── validation ── / function setErr(id, msg) { document.getElementById(id).textContent = msg; } function clearErr(id) { setErr(id, ""); }

window.humValidate = function() { let ok = true; clearErr("hum-temp-err"); clearErr("hum-rh-err"); clearErr("hum-pressure-err"); clearErr("hum-global-err");

const tempRaw = parseFloat(document.getElementById("hum-temp").value); const tempUnit = document.getElementById("hum-temp-unit").value; const rh = parseFloat(document.getElementById("hum-rh").value); const pressureRaw = document.getElementById("hum-pressure").value;

if (isNaN(tempRaw)) { setErr("hum-temp-err", "Enter a valid temperature."); ok = false; } else { const T_C = toC(tempRaw, tempUnit); if (T_C 60) { setErr("hum-temp-err", "Temperature must be between -60 °C and 60 °C (-76 °F – 140 °F)."); ok = false; } }

if (isNaN(rh) || rh 100) { setErr("hum-rh-err", "Relative humidity must be between 0% and 100%."); ok = false; }

if (pressureRaw !== "") { const p = parseFloat(pressureRaw); if (isNaN(p) || p 1100) { setErr("hum-pressure-err", "Pressure must be between 500 and 1100 hPa."); ok = false; } }

return ok; };

/ ── main calculation ── / window.humCalc = function() { if (!humValidate()) return;

const tempRaw = parseFloat(document.getElementById("hum-temp").value); const tempUnit = document.getElementById("hum-temp-unit").value; const rh = parseFloat(document.getElementById("hum-rh").value); const pressureRaw = document.getElementById("hum-pressure").value; const P_hPa = pressureRaw !== "" ? parseFloat(pressureRaw) : 1013.25; const outUnit = document.getElementById("hum-out-unit").value; const ul = unitLabel(outUnit);

const T_C = toC(tempRaw, tempUnit); const Td_C = dewPoint(T_C, rh); const Tw_C = wetBulb(T_C, rh); const AH = absoluteHumidity(T_C, rh); const SH = specificHumidity(T_C, rh, P_hPa); const e_s = esat(T_C); const e_a = (rh / 100) * e_s; const Hx = humidex(T_C, Td_C); const VPD = e_s - e_a;

const rows = [ ["Dew Point Temperature", fmt(fromC(Td_C, outUnit), 2) + " " + ul], ["Wet-Bulb Temperature", fmt(fromC(Tw_C, outUnit), 2) + " " + ul], ["Absolute Humidity", fmt(AH, 3) + " g/m³"], ["Specific Humidity", fmt(SH, 3) + " g/kg"], ["Saturation Vapor Pressure", fmt(e_s, 3) + " hPa"], ["Actual Vapor Pressure", fmt(e_a, 3) + " hPa"], ["Vapor Pressure Deficit (VPD)", fmt(VPD, 3) + " hPa"], ["Humidex (feels-like)", fmt(fromC(Hx, outUnit), 1) + " " + ul], ];

const tbody = document.getElementById("hum-result-body"); tbody.innerHTML = rows.map((r, i) => ${r[0]} ${r[1]} ).join("");

document.getElementById("hum-result").style.display = "block"; };

})();

#### Formulas Used

1. Saturation Vapor Pressure — Buck Equation:

es(T) = 6.1078 × exp( (17.625 × T) / (243.04 + T) )   [hPa]

2. Dew Point — Magnus Formula Inversion:

γ = ln(RH/100) + (17.625 × T) / (243.04 + T) Td = 243.04 × γ / (17.625 − γ)   [°C]

3. Absolute Humidity:

AH = 216.7 × ea / TK   [g/m³] where ea = (RH/100) × es,   TK = T + 273.15

4. Specific Humidity:

q = 621.97 × ea / (P − 0.378 × ea)   [g/kg]

5. Wet-Bulb Temperature — Stull (2011) Empirical:

Tw = T·atan(0.151977·√(RH+8.313659)) + atan(T+RH)        − atan(RH−1.676331) + 0.00391838·RH1.5·atan(0.023101·RH) − 4.686035

6. Vapor Pressure Deficit:

VPD = es − ea   [hPa]

7. Humidex (Environment Canada):

Humidex = T + 0.5555 × (es(Td) − 10.0)

#### Assumptions & References

• Dew point formula accuracy: ±0.35 °C for RH > 50% (Lawrence, 2005, BAMS).
• Wet-bulb formula: Stull, R. (2011). "Wet-Bulb Temperature from Relative Humidity and Air Temperature." Journal of Applied Meteorology and Climatology, 50(11), 2267–2269. Accuracy ±1 °C for 5–99% RH, −20 to 50 °C.

More Calculators

• Sports Calorie Burn Calculator
• Cloud Hosting Cost Estimator
• Website Performance Impact Calculator
• Software Development Cost Estimator
• Daily Calorie Needs Calculator
• Daily Water Intake Calculator

Read Next

Study Time Planner Authority Network America › Life Services Authority › National Calculator Authority .calc-container { max-width: 640px;...

References

• ANA
• Life Services Authority