Calculate humidity ratio, dew/frost point, enthalpy, specific volume and moist-air density from dry bulb, RH and pressure.
Trades & Professional Tools · HVAC
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Measured inputs · visitor-entered product and design assumptions
1EnterProvide the known values
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Use one consistent unit basis and measurements taken at the stated locations and operating condition. Enter project, manufacturer, fluid-property, pressure-temperature, efficiency, and test criteria from the actual system. Values stay in this browser.
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Calculate humidity ratio, dew/frost point, enthalpy, specific volume and moist-air density from dry bulb, RH and pressure.
Air state is more than temperature. Dry-bulb temperature, moisture, pressure, enthalpy, and airflow work together when air is mixed, cooled, heated, humidified, or dehumidified.
At a glance
See the HVAC relationship
Entering air state, process, and leaving air state. This is a simple reading map for this kind of calculation; it does not represent a complete installed system.
Dry-bulb temperature (-80 to 50°C)Relative humidity, water at ≥0°C / ice at <0°C (%)Absolute pressure (kPa)
The relationship
The formula used here
Properties use water-vapor saturation pressure, w=0.621945pv/(p−pv), and h=1.006T+w(2501+1.86T); RH is relative to water at ≥0°C and ice below 0°C.
This calculator applies that relationship to your entries. Use the formula to check that the units, reference condition, and measurement location make sense together.
Field reading
Use the result as a next check
1. Describe one real condition
Enter values from the same system state, period, unit basis, and measurement location.
2. Read the relationship
Use measured or documented state points, keep the pressure basis explicit, and read sensible and moisture-related outputs separately before combining them.
3. Keep the boundary clear
It does not establish comfort, mould, condensation, indoor-air-quality, coil selection, or humidity-control requirements.
Quick guide
How to use this calculator
Choose the calculation mode or measurement system that matches the values you actually have.
Enter measured project dimensions and use product-specific coverage, density, yield, resistance, or waste data where requested.
Review the intermediate results before ordering material or applying the result on site.
Calculation method
Calculation method
Properties use water-vapor saturation pressure, w=0.621945pv/(p−pv), and h=1.006T+w(2501+1.86T); RH is relative to water at ≥0°C and ice below 0°C.
The calculator preserves full internal precision and rounds only displayed results. Quantity outputs round up when whole purchasable pieces are required.
Worked example
Worked example
20°C, 50% RH at 101.325 kPa has humidity ratio about 0.00726 kg/kg.
Properties use water-vapor saturation pressure, w=0.621945pv/(p−pv), and h=1.006T+w(2501+1.86T); RH is relative to water at ≥0°C and ice below 0°C.
Supported inputs
Precision and limits
HVAC design and service boundary
HVAC results use the measured, design, manufacturer, psychrometric, fluid-property, pressure-temperature, efficiency, and test values you enter. They do not perform or certify Manual J, D, or S procedures; supply ventilation or code defaults; select equipment; identify refrigerant; determine a safe charge; authorize combustion, pressure, electrical, or refrigerant work; or replace approved manufacturer data and a qualified HVAC professional.
Planning scope
This calculator supports measurement, estimating, and scenario planning. It does not inspect a site, select a product, certify a design, or replace drawings, specifications, manufacturer instructions, local codes, permits, or a qualified trade professional.
Measured and product-specific inputs
Nominal dimensions can differ from actual dimensions. Verify inside pipe diameters, actual lumber sizes, product coverage, bag yield, material density, conductor resistance, waste, and packaging against the materials used on the project.
Safety and regulatory limits
Electrical, HVAC, structural, excavation, roofing, pressure, lifting, and life-safety work may require jurisdiction-specific calculations and professional approval. Do not use a generic planning result as a code-compliance or safety determination.
Precision and privacy
Inputs accept bounded plain decimals. Calculations remain in this browser and raw entered project values are not submitted to 365CALCS.COM.
