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# STP - Standard Temperature and Pressure and NTP - Normal Temperature and Pressure

Since temperature and air pressure varies from place to place a standard reference is necessary for comparing the testing and the documentation of chemical and physical processes.

Note! There is a variety of alternative definitions for standard reference conditions of temperature and pressure. STP, NTP and other definitions should therefore be used with care. It is always important to know the reference temperature and reference pressure for the actual definition used.

### STP - Standard Temperature and Pressure

STP is commonly used to define standard conditions for temperature and pressure which is important for the measurements and documentation of chemical and physical processes:

1. STP - Standard Temperature and Pressure - is defined by IUPAC (International Union of Pure and Applied Chemistry) as air at 0 oC (273.15 K, 32 oF) and 105 pascals (1 bar).
2. STP - commonly used in the Imperial and USA system of units - as air at 60 oF (520 o R, 15.6 oC ) and 14.696 psia (1 atm,  1.01325 bara)
• also named "1 Standard Atmosphere"
• At these conditions, the volume of 1 mol of a gas is 23.6442 liters.
• These conditions are the most commonly used to define the volume term Sm3 (Standard cubic meter)

Note! The earlier IUAPC definition of STP to 273.15 K and 1 atm (1.01325 105 Pa) is discontinued.  However,

• These conditions are still the most commonly used to define the volume term Nm3 (Normal cubic meter)
• At these conditions, the volume of 1 mol of a gas is 22.4136 liters.

1 Pa = 10-6 N/mm2= 10 -5 bar = 0.1020 kp/m2= 1.02x10-4 m H2O = 9.869x10-6 atm = 1.45x10-4 psi (lbf/in2)

### NTP - Normal Temperature and Pressure

NTP is commonly used  as a standard condition  for testing and documentation of fan capacities:

• NTP - Normal Temperature and Pressure - is defined as air at 20 oC (293.15 K, 68 oF) and 1 atm ( 101.325 kN/m2, 101.325 kPa, 14.7 psia, 0 psig, 29.92 in Hg, 407 in H2O, 760 torr). Density 1.204 kg/m3 (0.075 pounds per cubic foot)
• At these conditions, the volume of 1 mol of a gas is 24.0548 liters.

#### Example - Fan Pressure Increase

A fan that produce a static pressure of 3 in H2O (a good average value) - will increase the absolute air pressure by

((3 in H2O) / (407 in H2O)) (100 %) = 0.74 %

### SATP - Standard Ambient Temperature and Pressure

SATP - Standard Ambient Temperature and Pressure is also used in chemistry (International Union of Pure and Applied Chemistry - IUPAC) as a reference:

• SATP - Standard Ambient Temperature and Pressure is a reference with temperature of 25 oC (298.15 K) and pressure of 100.000 kPa.
• At these conditions, the volume of 1 mol of a gas is 24.4651 liters.

### ISA - International Standard Atmosphere

ISA - International Standard Atmosphere is used as a reference to aircraft performance:

• ISA - International Standard Atmosphere is defined to 101.325 kPa, 15 oC and 0% humidity.

### ICAO Standard Atmosphere

Standard model of the atmosphere adopted by the International Civil Aviation Organization (ICAO):

• Atmospheric pressure: 760 mmHg = 14.7 lbs-force/sq inch
• Temperature: 15 oC = 288.15 K = 59 oF

## Related Topics

### • Basics

Basic engineering data. SI-system, unit converters, physical constants, drawing scales and more.

### • Material Properties

Properties of gases, fluids and solids. Densities, specific heats, viscosities and more.

### • Ventilation Systems

Design of systems for ventilation and air handling - air change rates, ducts and pressure drops, charts and diagrams and more.

## Related Documents

### Acetone - Thermophysical Properties

Chemical, physical and thermal properties of acetone, also called 2-propanone, dimethyl ketone and pyroacetic acid. Phase diagram included.

### Air - Density and Specific Volume vs. Altitude

Density and specific volume of air varies with elevation above sea level.

### Air - Humidity Measurement from Dry and Wet Bulb Temperature

Relative humidity in moist air can estimated by measuring the dry and wet bulb temperature.

### Air - Psychrometric Chart for Standard Atmospheric Conditions - Imperial Units

Psychrometric chart for air at barometric pressure 29.921 inches of Mercury and temperature ranging 20oF to 120oF.

### Air - Specific Heat vs. Pressure at Constant Temperature

Figures and tables with isobaric (Cp) and isochoric (Cv) specific heat of air at constant temperature and pressure ranging 0.01 to 10000 bara.

### Air - Thermal Conductivity vs. Temperature and Pressure

Online calculator with figures and tables showing air thermal conductivity vs. temperature and pressure. SI and imperial units.

### Air - Thermophysical Properties

Thermal properties of air at different temperatures - density, viscosity, critical temperature and pressure, triple point, enthalpi and entropi, thermal conductivity and diffusivity and more.

### Air Ducts - Major Friction Loss vs. Temperature and Pressure

The influence of temperature and air pressure on major friction loss.

### Atmospheric Pressure vs. Elevation above Sea Level

Elevation above sea level - in feet and meter - with barometric and atmospheric pressure - inches mercury, psia, kg/cm2 and kPa.

### Barometer - Altitude Compensation

Elevation compensating manometer.

### Benzene - Dynamic and Kinematic Viscosity vs. Temperature and Pressure

Online calculator, figures and table showing dynamic and kinematic viscosity of benzene, C6H6, at varying temperature and pressure - Imperial and SI Units.

### Benzene - Thermophysical properties

Chemical, physical and thermal properties of benzene, also called benzol. Phase diagram included.

### Density vs. Specific Weight and Specific Gravity

An introduction to density, specific weight and specific gravity.

### Dry Air and Water Vapor - Density and Specific Volume vs. Temperature - Imperial Units

Density and specific volume of dry air and water vapor at temperatures ranging 225 to 900 degF (107 to 482 degC).

### Ethanol - Dynamic and Kinematic Viscosity vs. Temperature and Pressure

Online calculator, figures and tables showing dynamic and kinematic viscosity of ethanol, C2H5OH, at varying temperature and pressure - Imperial and SI Units.

### Ethylene - Thermophysical Properties

Chemical, physical and thermal properties of ethylene, also called ethene, acetene and olefiant gas. Phase diagram included.

### Fan Affinity Laws

The affinity laws can be used to calculate resulting volume capacity, head or power consumption when speed or wheel diameters are changed.

### Fans - Volume Flow, Pressure Head and Power Consumption vs. Air Temperature and Density

The temperature and density of the air influences on the volume flow, pressure head and power consumption in a fan.

### Gases - Densities

Densities and molecular weights of common gases like acetylene, air, methane, nitrogen, oxygen and others.

### Gases - Specific Gravities

Specific gravities of air, ammonia, butadiene, carbon dioxide, carbon monoxide and some other common gases.

### Indoor Conditions - Summer or Winter

Recommended indoor design conditions summer or winter.

### International Standard Atmosphere

International standard atmosphere in elevation -2000 to 30000 metre - pressure, temperature, density, viscosity, thermal conductivity and velocity of sound.

### Methane - Dynamic and Kinematic Viscosity vs. Temperature and Pressure

Online calculator, figures and tables showing dynamic and kinematic viscosity of methane, CH4, at varying temperature and pressure - Imperial and SI Units.

### Pressure Units - Online Converter

Convert between pressure units like Pa,  bar, atmosphere, pound square feet, psi and more.

### Pressure Units Converter

Convert from kPa to psi and inches of Water and Mercury.

### Saturated Steam - Properties - Imperial Units

Steam table with sensible, latent and total heat, and specific volume at different gauge pressures and temperatures.

### Thermocouples

Thermocouples - types, principles and temperature ranges.

### U.S. Standard Atmosphere vs. Altitude

Properties of the US standard atmosphere ranging -5000 to 250000 ft altitude.

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