| Centipascals (cPa) | Terapascals (TPa) |
|---|---|
| 1 Centipascal | 1 × 10-14 TPa |
| 2 Centipascals | 2 × 10-14 TPa |
| 3 Centipascals | 3 × 10-14 TPa |
| 4 Centipascals | 4 × 10-14 TPa |
| 5 Centipascals | 5 × 10-14 TPa |
| 10 Centipascals | 1 × 10-13 TPa |
| 20 Centipascals | 2 × 10-13 TPa |
| 25 Centipascals | 2.5 × 10-13 TPa |
| 50 Centipascals | 5 × 10-13 TPa |
| 100 Centipascals | 1 × 10-12 TPa |
| Reference | Centipascals (cPa) | Terapascals (TPa) |
|---|---|---|
| Atmospheric pressure at sea level | 10132500 cPa | 0.000000101325 TPa |
| Healthy blood pressure (120 mmHg) | 1600000 cPa | 0.000000016 TPa |
| A car tyre | 22000000 cPa | 0.00000022 TPa |
| A racing bicycle tyre | 60000000 cPa | 0.0000006 TPa |
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.
The terapascal is a unit of pressure equal to a thousand gigapascals, written TPa. It is ten million bar. Nothing built by engineers operates at this pressure, and the unit belongs instead to two quite separate corners of science: the stiffness of the strongest materials known, and the interiors of large planets.
Carbon nanostructures put it on the map. A single-walled carbon nanotube has a Young's modulus close to one terapascal, and a sheet of graphene the same, which makes them the stiffest materials ever measured relative to their weight. Diamond, long the benchmark, comes in at 1.2 terapascals. Those three numbers are the reason the unit appears at all in materials science.
Stiffness at this level is not the same as strength. A nanotube resists stretching enormously, but a real fibre made of many of them fails at a far lower stress because the tubes slide past one another. Confusing a terapascal modulus with a terapascal breaking strength is one of the commonest errors in popular accounts of these materials.
Planetary interiors reach genuine terapascal pressures. The centre of Jupiter is estimated at three to four terapascals, and the cores of larger gas giants beyond that. Under such conditions hydrogen behaves as a metal, which is what generates the planet's magnetic field, so the unit describes a state of matter rather than a load on a structure.
Laboratories can now reach it briefly. Laser-driven shock compression and pulsed magnetic techniques drive samples into the terapascal range for nanoseconds at a time, long enough to record how a material's density and structure respond. Those experiments are the only direct evidence available about matter under the conditions inside giant planets.
For scale, one terapascal is ten million times atmospheric pressure and about a thousand times the pressure at the centre of the earth divided by three. The number stops being something a person can feel and becomes a description of what atoms do when they are pushed close enough together to change their chemistry.
One terapascal equals 1,000,000,000,000 pascals, 1000 gigapascals, 10,000,000 bar, or about 145 million pounds per square inch.