Pounds per square inch

The pound per square inch or, more accurately, pound-force per square inch (symbol: lbf/in2;[1] abbreviation: psi) is a unit of pressure or of stress based on avoirdupois units. It is the pressure resulting from a force of one pound-force applied to an area of one square inch. In SI units, 1 psi is approximately equal to 6895 N/m2.

Pounds per square inch absolute (psia) is used to make it clear that the pressure is relative to a vacuum rather than the ambient atmospheric pressure. Since atmospheric pressure at sea level is around 14.7 psi, this will be added to any pressure reading made in air at sea level. The converse is pounds per square inch gauge (psig), indicating that the pressure is relative to atmospheric pressure. For example, a bicycle tire pumped up to 65 psig in a local atmospheric pressure at sea level (14.7 psia) will have a pressure of 79.7 psia (14.7 psi + 65 psi).[2][3] When gauge pressure is referenced to something other than ambient atmospheric pressure, then the units would be pounds per square inch differential (psid).

Pound per square inch
A pressure gauge reading in psi (red scale) and kPa (black scale)
General information
Unit systemImperial units, US customary units
Unit ofPressure, Stress
Symbolpsi or lbf/in2
1 psi in ...... is equal to ...
   SI units   6.894757 kPa


The kilopound per square inch (ksi) is a scaled unit derived from psi, equivalent to a thousand psi (1000 lbf/in2).

ksi are not widely used for gas pressures. They are mostly used in materials science, where the tensile strength of a material is measured as a large number of psi.[4]

The conversion in SI Units is 1 ksi = 6.895 MPa, or 1 MPa = 0.145 ksi.

The megapound per square inch (Mpsi) is another multiple equal to a million psi. It is used in mechanics for the elastic modulus of materials, especially for metals.[5]

The conversion in SI Units is 1 Mpsi = 6.895 GPa, or 1 GPa = 0.145 Mpsi.



The exact conversions to and from SI are, by definition:

1 psi = (4.4482216152605 / 0.00064516) Pa

1 Pa = (0.00064516 / 4.4482216152605) psi

As the pascal is very small unit, relative to industrial pressures, the kilopascal is commonly used. 1000 kPa = 147 psi.

Approximate conversions (rounded to some arbitrary number of digits, except when denoted by "≡") are shown in the following table.

Pressure units
Pascal Bar Technical atmosphere Standard atmosphere Torr Pounds per square inch
(Pa) (bar) (at) (atm) (Torr) (lbf/in2)
1 Pa ≡ 1 N/m2 10−5 1.0197×10−5 9.8692×10−6 7.5006×10−3 0.000 145 037 737 730
1 bar 105 ≡ 100 kPa

≡ 106 dyn/cm2

1.0197 0.98692 750.06 14.503 773 773 022
1 at 98066.5 0.980665 ≡ 1 kgf/cm2 0.967 841 105 354 1 735.559 240 1 14.223 343 307 120 3
1 atm 101325 1.01325 1.0332 1 760 14.695 948 775 514 2
1 Torr 133.322 368 421 0.001 333 224 0.001 359 51 1/760 ≈ 0.001 315 789 1 Torr

≈ 1 mmHg

0.019 336 775
1 lbf/in2 6894.757 293 168 0.068 947 573 0.070 306 958 0.068 045 964 51.714 932 572 ≡ 1 lbf/in2

See also


  1. ^ IEEE Standard Letter Symbols for Units of Measurement (SI Units, Customary Inch-Pound Units, and Certain Other Units), IEEE Std 260.1™-2004 (Revision of IEEE Std 260.1-1993)
  2. ^ "Glossary of Industrial Air Cleaning Technology". United Air Specialists, Inc. Archived from the original on August 1, 2011.
  3. ^ "Gage v. Sealed v. Absolute pressure" (PDF). Dynisco.
  4. ^ "Tensile Strength of Steel and Other Metals". All Metals & Forge Group. Retrieved 2016-07-26. A metal’s yield strength and ultimate tensile strength values are expressed in tons per square inch, pounds per square inch or thousand pounds (KSI) per square inch. For example, a tensile strength of a steel that can withstand 40,000 pounds of force per square inch may be expressed as 40,000 PSI or 40 KSI (with K being the [multiplier] for thousands of pounds). The tensile strength of steel may also be shown in MPa, or megapascal.
  5. ^ An example of the use of Mpsi in mechanics for the elastic moduli of several materials

External links

Bar (unit)

The bar is a metric unit of pressure, but is not approved as part of the International System of Units (SI). It is defined as exactly equal to 100,000 Pa, which is slightly less than the current average atmospheric pressure on Earth at sea level.The bar and the millibar were introduced by the Norwegian meteorologist Vilhelm Bjerknes, who was a founder of the modern practice of weather forecasting.The International Bureau of Weights and Measures (BIPM) lists the bar as one of the "non-SI units [that authors] should have the freedom to use", but has declined to include it among the "Non-SI units accepted for use with the SI". The bar has been legally recognised in countries of the European Union since 2004. The US National Institute of Standards and Technology (NIST) deprecates its use except for "limited use in meteorology" and lists it as one of several units that "must not be introduced in fields where they are not presently used". The International Astronomical Union (IAU) also lists it under "Non-SI units and symbols whose continued use is deprecated".Units derived from the bar include the megabar (symbol: Mbar), kilobar (symbol: kbar), decibar (symbol: dbar), centibar (symbol: cbar), and millibar (symbol: mbar or mb). The notation bar(g), though deprecated by various bodies, represents gauge pressure, i.e., pressure in bars above ambient or atmospheric pressure.

Bertha (drag boat)

Bertha is a steam-powered boat built in 1844 to remove silt from the Port of Bridgwater in Somerset, England. It is the oldest operational steam vessel in Britain, and possibly in the world. It is part of the National Historic Fleet.The boat was built, of riveted iron, in Bristol by Lunnel, G & Co copying a design, by John McLean, developed by Isambard Kingdom Brunel to deal with silt in the Floating Harbour. It is a Bed leveler or plough dredger, with a large metal blade, which could be lowered at the stern of the boat, below the water similar to a bulldozer on land.Bertha is 50 feet (15 m) long and 15.5 feet (4.7 m) wide, with a tonnage of 60 tons.a The power is from a coal fired single cylinder steam engine providing steam at 40 pounds per square inch (280 kPa). A large flywheel and drive shaft drove a single-reduction spur wheel drive. It moved by being pulled along chains anchored on the quay.Bertha worked in Bridgwater Docks, after the connection of the Bridgwater and Taunton Canal to the River Parrett, from 1844 until 1969. The vessel was initially owned by the Great Western Railway and then British Railways. She was then taken to the Exeter Maritime Museum. In 1997 it moved to the World of Boats at Eyemouth where it is being restored.

Boil-water advisory

A boil-water advisory or boil-water order is a public health advisory or directive given by government or health authorities to consumers when a community's drinking water is, or could be, contaminated by pathogens.Under a boil-water advisory (BWA), the Centers for Disease Control and Prevention recommends that water be brought to a rolling boil for one minute before it is consumed in order to kill protozoa, bacteria and viruses. At altitudes above 2,000 metres (6,600 ft), boiling should be extended to 3 minutes, as the lower boiling point at high altitudes requires more time to kill such organisms.

BWAs are typically issued when monitoring of water being served to consumers detects Escherichia coli or other microbiological indicators of sewage contamination. Another reason for a BWA is a failure of distribution system integrity evidenced by a loss of system pressure. While loss of pressure does not necessarily mean the water has been contaminated, it does mean that pathogens may be able to enter the piped-water system and thus be carried to consumers. In the United States, this has been defined as a drop below 20 pounds per square inch (140 kPa).

Boiler water

Boiler water is the liquid phase of steam within a boiler. The term may also be applied to raw water intended for use in boilers, treated boiler feedwater, steam condensate being returned to a boiler, or boiler blowdown being removed from a boiler.

Cockle Creek Power Station

Cockle Creek Power Station was located in Teralba, New South Wales, Australia on the banks of Cockle Creek. The power stationed operated from 11 March 1927 until March 1976.

Copper units of pressure

Copper units of pressure or CUP, and the related lead units of pressure or LUP, are terms applied to pressure measurements used in the field of internal ballistics for the estimation of chamber pressures in firearms. These terms were adopted by convention to indicate that the pressure values were measured by copper crusher and lead crusher gauges respectively. In recent years, they have been replaced by the adoption of more modern piezoelectric pressure gauges that more accurately measure chamber pressures and generally give significantly higher pressure values. This nomenclature was adopted to avoid confusion and the potentially dangerous interchange of pressure values and standards made by different types of pressure gauges. Pressure is a fundamental thermodynamic parameter that is expressed in units of force divided by area. In the avoirdupois system, the units of pressure are pounds per square inch and in the metric system, the units or pressure are newtons per square meter (pascals). A chamber pressure measured with a copper crusher gauge would be expressed as psi (CUP) in the English system or MPa (CUP) in the metric system.

Drafting water

The term drafting water refers to the use of suction to move a liquid such as water from a vessel or body of water below the intake of a suction pump. A rural fire department or farmer might draft water from a pond as the first step in moving the water elsewhere. A suction pump creates a partial vacuum (a "draft") and the atmospheric pressure on the water's surface forces the water into the pump, usually via a rigid pipe (sometimes called a dry hydrant) or a semi-rigid hard suction hose.Standard atmospheric pressure is 101 kPa (14.7 lbf/in²) and that can only raise water to a theoretical maximum of 10.3 metres (33.9 ft). Depending on application, fire department pumps lift water 6 to 10 metres (20 to 30 ft).

To reduce drafting friction and obtain a larger flow or higher lift, a larger cross-section of suction hose is employed. For example, using a five-inch (127 mm) hose, a pump that could lift 500 US gallons per minute (30 L/s) up 23 feet (7 m) would only be able to lift the same amount of water 12.5 feet (4 m) through a 3.5-inch (76 mm) hose. Fire engines are often seen carrying two or three 10-foot (3 m) lengths of suction hose, but the longer the lift, the lower the flow, for a fixed-diameter suction hose and a given pump. Multiple relays could be used if the need arises, with a suction pump drafting up to 10 metres (30 ft) and discharging at great distances.

It is also possible to use a gravity siphon to draft water for a small lift, and this technique is often used in forest fire suppression, where portable reservoirs of 1,000 to 3,000 US gallons (5 to 10 m³) are filled with water and small hoses are used downhill of the tanks. The nozzle pressure is proportional to its distance below the reservoir surface. Forty-three percent of the distance, in feet, is approximately the number of pounds per square inch pressure (e.g., 100 feet lower: 43 psi). The tank may itself be gravity-fed through hoses from a nearby water source, or by pumps or helicopters delivering water from further away.

Estimated pore pressure

Estimated pore pressure, as used in the oil industry and mud logging, is an approximation of the amount of force that is being exerted into the borehole by fluids or gases within the formation that has been penetrated.In the oil industry, estimated pore pressure is measured in pounds per square inch (psi), but is converted to equivalent mud weight and measured in pounds per gallon (lb/gal) to more easily determine the amount of mud weight required to prevent the fluid or gas from escaping and causing a blowout or wellbore failure.

Ground pressure

Ground pressure is the pressure exerted on the ground by the tires or tracks of a motorized vehicle, and is one measure of its potential mobility, especially over soft ground. It also applies to the feet of a walking person or machine. Ground pressure is measured in pascals (Pa) which corresponds to the United States customary units unit of pounds per square inch (psi). Average ground pressure can be calculated using the standard formula for average pressure: P = F/A. In an idealized case, i.e. a static, uniform net force normal to level ground, this is simply the object's weight divided by contact area. The ground pressure of motorized vehicles is often compared to the ground pressure of a human foot, which can be 60 - 80 kPa while walking or as much as 13 MPa for a person in spike heels.Increasing the size of the contact area on the ground (the footprint) in relation to the weight decreases the ground pressure. Ground pressure of 14 kPa (2 psi) or less is recommended for fragile ecosystems like marshes. Decreasing the ground pressure increases the flotation, allowing easier passage of the body over soft terrain. This is often observed in activities like snowshoeing.

Inch of water

Inches of water, inches of water gauge (iwg or in.w.g.), inches water column (inch wc or just wc), inAq, Aq, or inH2O is a non-SI unit for pressure. The units are conventionally used for measurement of certain pressure differentials such as small pressure differences across an orifice, or in a pipeline or shaft. Inches of water can be converted to a pressure unit using the formula for pressure head.

It is defined as the pressure exerted by a column of water of 1 inch in height at defined conditions. At a temperature of 4 °C (39.2 °F) pure water has its highest density (1000 kg/m3). At that temperature and assuming the standard acceleration of gravity, 1 inAq is approximately 249.082 pascals.Alternative standard conditions in uncommon usage are 60 °F, or 68 °F (20 °C), and depends on industry standards rather than on international standards.

In North America, air and other industrial gasses are often measured in inches of water when at low pressure. This is in contrast to inches of mercury or pounds per square inch (psi, lbf/in2) for larger pressures. One usage is in the measurement of air ("wind") that supplies a pipe organ and is referred simply as inches. It is also used in natural gas distribution for measuring utilization pressure (U.P., i.e. the residential point of use) which is typically between 6 and 7 inches WC (6~7″ WC) or about 0.25 lbf/in2.

1 inAq ≈ 0.036 lbf/in2, or 27.7 inAq ≈ 1 lbf/in2.

John Purroy Mitchel (fireboat)

The John Purroy Mitchel was a fireboat operated by the FDNY. She was named after former mayor of New York City, John Purroy Mitchel. Grace Drennan, niece of Fire Commissioner Thomas J. Drennan played a ceremonial role in the vessels launch on July 24, 1921. Her launch was also attended by current mayor John Francis Hylan.

The John Purroy Mitchel was the city's first fireboat powered by fuel-oil, not coal. She was 132 feet (40 m) long, and her pumps could throw 9,000 gallons per minute, at pressure of 300 pounds per square inch. One of her water cannons was mounted on top of a 26 feet (7.9 m) tower.

The John Purroy Mitchel was built by Standard Shipbuilding Corporation, of Shooter's Island, and was budgeted at $220,000, but came in under budget, at $200,000.

Mark III (space suit)

The Mark III or MK III (H-1) is a NASA space suit technology demonstrator built by ILC Dover. While heavier than other suits (at 59 kilograms (130 lb), with a 15 kilograms (33 lb) Primary Life Support System backpack), the Mark III is more mobile, and is designed for a relatively high operating pressure.The Mark III is a rear-entry suit, unlike the EMU currently in use, which is a waist-entry suit. The suit incorporates a mix of hard and soft suit components, including hard upper torso, hard lower torso and hip elements made of graphite/epoxy composite, bearings at the shoulder, upper arm, hip, waist, and ankle, and soft fabric joints at the elbow, knee, and ankle.

The 8.3 pounds per square inch (57 kPa) operating pressure of the Mark III makes it a "zero-prebreathe" suit, meaning that astronauts would be able to transition directly from a one atmosphere, mixed-gas space station environment, such as that on the International Space Station, to the suit, without risk of the bends, which can occur with rapid depressurization from an atmosphere containing nitrogen or another inert gas. Currently, astronauts must spend several hours in a reduced pressure, pure oxygen environment before EVA to avoid these risks.


Overpressure (or blast overpressure) is the pressure caused by a shock wave over and above normal atmospheric pressure. The shock wave may be caused by sonic boom or by explosion, and the resulting overpressure receives particular attention when measuring the effects of nuclear weapons or thermobaric bombs.

Pressure washing

Pressure washing or power washing is the use of high-pressure water spray to remove loose paint, mold, grime, dust, mud, chewing gum and dirt from surfaces and objects such as buildings, vehicles and concrete surfaces. The volume of a mechanical pressure washer is expressed in gallons or litres per minute, often designed into the pump and not variable. The pressure, expressed in pounds per square inch, pascals, or bar, is designed into the pump but can be varied by adjusting the unloader valve. Machines that produce pressures from 750 to 30,000 psi (5 to 200 MPa) or more are available.

The terms pressure washing and power washing are used interchangeably in many scenarios, and there is some debate as to whether or not they are actually different processes.

A pressure washing surface cleaner is a tool consisting of two to four high-pressure jets on a rotating bar that swivels when water is flowing. This action creates a uniformed cleaning pattern that can clean flat surfaces at a rapid rate.

Hydro-jet cleaning is a more powerful form of power washing, employed to remove buildup and debris in tanks and lines.


SkyPoint is a 361 ft (110 m) high rise in Tampa, Florida. It was constructed from 2005 to 2007 and has 33 floors. The Preston Partnership, LLC along with Echelon Engineering, LLC designed the building, which is the 9th tallest building in Tampa. It has 380 Residential units spread across 25 levels sitting atop seven levels of enclosed parking. The ground floor houses 10,800 square feet (1,000 m2) of retail space. Separating the parking levels from the residential is a large amenity deck that houses a 4,000 square feet (370 m2) clubhouse, a 2,500 square feet (230 m2) fitness center, a media room and lounge, as well as a large landscaped terrace and swimming pool. Skypoint is composed of cast-in-place concrete in conjunction with post-tensioned cables. Concrete strengths range from 5,000 pounds per square inch (34,000 kPa) at typical residential floors up to 10,000 pounds per square inch (69,000 kPa) at the ground level columns and shearwalls. Just before its grand opening to residents, William “Wild Bill” Stroup BASE-jumped off the building on March 6, 2007.

The Russel Middlebrook Series

The Russel Middlebrook Series is a series of young adult fiction novels written by Brent Hartinger. The series follows the lives and love lives of Russel Middlebrook and his friends as they create the Geography Club, a safe space for gay teenagers and eventually the first Gay-Straight-Bisexual Alliance at their school.

Torsion (mechanics)

In the field of solid mechanics, torsion is the twisting of an object due to an applied torque. Torsion is expressed in either the Pascal (Pa), an SI unit for newtons per square metre, or in pounds per square inch (psi) while torque is expressed in newton metres (N·m) or foot-pound force (ft·lbf). In sections perpendicular to the torque axis, the resultant shear stress in this section is perpendicular to the radius.

In non-circular cross-sections, twisting is accompanied by a distortion called warping, in which transverse sections do not remain plane. For shafts of uniform cross-section unrestrained against warping, the torsion is:


Tosin Abasi

Oluwatosin Ayoyinka Olumide "Tosin" Abasi (born January 7, 1983), is a Nigerian American musician, best known as the founder and lead guitarist of the instrumental progressive metal band Animals as Leaders. Before founding Animals as Leaders, he was the guitarist for the technical metalcore band Reflux. He has recorded and released four albums with Animals as Leaders: a self-titled debut, Weightless, The Joy of Motion and their most recent album, The Madness of Many. A guitar virtuoso, Guitar World ranks Abasi at #97 on their list of 100 Greatest Guitarists of all time.

Ultimate tensile strength

Ultimate tensile strength (UTS), often shortened to tensile strength (TS), ultimate strength, or Ftu within equations, is the capacity of a material or structure to withstand loads tending to elongate, as opposed to compressive strength, which withstands loads tending to reduce size. In other words, tensile strength resists tension (being pulled apart), whereas compressive strength resists compression (being pushed together). Ultimate tensile strength is measured by the maximum stress that a material can withstand while being stretched or pulled before breaking. In the study of strength of materials, tensile strength, compressive strength, and shear strength can be analyzed independently.

Some materials break very sharply, without plastic deformation, in what is called a brittle failure. Others, which are more ductile, including most metals, experience some plastic deformation and possibly necking before fracture.

The UTS is usually found by performing a tensile test and recording the engineering stress versus strain. The highest point of the stress–strain curve (see point 1 on the engineering stress–strain diagrams below) is the UTS. It is an intensive property; therefore its value does not depend on the size of the test specimen. However, it is dependent on other factors, such as the preparation of the specimen, the presence or otherwise of surface defects, and the temperature of the test environment and material.

Tensile strengths are rarely used in the design of ductile members, but they are important in brittle members. They are tabulated for common materials such as alloys, composite materials, ceramics, plastics, and wood.

Tensile strength can be defined for liquids as well as solids under certain conditions. For example, when a tree draws water from its roots to its upper leaves by transpiration, the column of water is pulled upwards from the top by the cohesion of the water in the xylem, and this force is transmitted down the column by its tensile strength. Air pressure, osmotic pressure, and capillary tension also plays a small part in a tree's ability to draw up water, but this alone would only be sufficient to push the column of water to a height of less than ten metres, and trees can grow much higher than that (over 100 m).

Tensile strength is defined as a stress, which is measured as force per unit area. For some non-homogeneous materials (or for assembled components) it can be reported just as a force or as a force per unit width. In the International System of Units (SI), the unit is the pascal (Pa) (or a multiple thereof, often megapascals (MPa), using the SI prefix mega); or, equivalently to pascals, newtons per square metre (N/m²). A United States customary unit is pounds per square inch (lb/in² or psi), or kilo-pounds per square inch (ksi, or sometimes kpsi), which is equal to 1000 psi; kilo-pounds per square inch are commonly used in one country (US), when measuring tensile strengths.

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