Conversion from Gigapascals to Centipascals

Information about the Gigapascal (GPa)

The gigapascal is a unit of pressure equal to a billion pascals, written GPa. It is a thousand megapascals and ten thousand bar. It is the unit in which materials science states stiffness rather than strength, and in which the pressures inside planets and inside high-pressure laboratories are described.

Elastic modulus is its principal use. Steel has a Young's modulus of about 200 gigapascals, copper 117, aluminium 70, ordinary glass 70, concrete around 30, timber along the grain 10 to 15, and rubber less than a tenth of one. Those numbers describe how much a material stretches under load, not when it breaks, and they explain why a steel beam of the same strength as an aluminium one still deflects less.

Diamond marks the top of the ordinary scale. Its modulus of roughly 1200 gigapascals is the highest of any natural material, which is why it is used to make anvils for high-pressure work: nothing else can push that hard without deforming first. Synthetic diamond is made industrially at about five gigapascals and high temperature, in presses built specifically to hold that pressure.

The interior of the earth is described in the same unit. Pressure at the base of the crust is around one gigapascal, at the boundary between mantle and core about 136, and at the centre of the planet roughly 360. Laboratory diamond anvil cells now reach and exceed the central value, which allows the behaviour of iron and silicates under planetary conditions to be studied directly rather than inferred.

For contrast, the deepest point in the ocean exerts only about 0.11 gigapascals. That comparison is worth keeping, because it shows how much larger geological pressures are than anything associated with water: the bottom of the Mariana Trench is a thousandth of the pressure at the centre of the earth.

Below the gigapascal, the megapascal describes strength, and above it there is little except stellar and theoretical physics. The terapascal appears mainly in the elastic modulus of carbon nanotubes and in the interiors of giant planets, so the gigapascal is effectively the top of the range that laboratories and engineers work in.

One gigapascal equals 1,000,000,000 pascals, 1000 megapascals, 10,000 bar, or about 145,000 pounds per square inch.

Information about the Centipascal (cPa)

The centipascal is a unit of pressure equal to one hundredth of a pascal. Its symbol is cPa. It is a legitimate metric combination that almost nobody writes, and understanding why it is unused says more about how pressure is actually recorded than a list of its applications ever could.

The centi prefix has one great success behind it, the centimetre, and that success came from the human scale of the metre. A metre is too long for the width of a hand and a millimetre too short, so the centimetre filled a real gap. Pressure has no comparable gap. The pascal is already so small that dividing it further gives numbers no instrument in ordinary use can resolve.

A centipascal is one hundredth of the pressure of a sheet of paper on a table. It is the pressure difference across a millimetre of air, or roughly what a grain of sand exerts spread over a fingernail. Nothing in engineering, meteorology or building practice needs that resolution: airtightness testing works at fifty pascals, ventilation at a few hundred, and weather at tens of thousands.

Where pressures smaller than a pascal do matter — acoustics and vacuum work — the convention jumps straight to the millipascal and the micropascal, because those fit the thousand-step ladder that the rest of the measurement system uses. A sound pressure of 20 millipascals is written that way rather than as 2 centipascals, even though the two are the same, because everything around it on the page is in thousand-step units.

The unit is nevertheless well defined, and that is the metric system working as designed. Every prefix combines with every unit without exception, so a reader who has never seen cPa can still decode it on sight from the prefix alone. A system with gaps would require a table; a system without them requires only the rule.

Occasional appearances do occur. Older instrument manuals sometimes use it, some national standards mention it in passing, and a few specialist fields adopt it locally when their numbers happen to fall between one and a hundred in that unit. A converter has to handle it for exactly those cases.

One centipascal equals 0.01 pascals, 10 millipascals, 0.1 decipascals, or about 0.00000145 pounds per square inch.