| Pascals (Pa) | Newtons per square meter (N/m²) |
|---|---|
| 1 Pascal | 1 N/m² |
| 2 Pascals | 2 N/m² |
| 3 Pascals | 3 N/m² |
| 4 Pascals | 4 N/m² |
| 5 Pascals | 5 N/m² |
| 10 Pascals | 10 N/m² |
| 20 Pascals | 20 N/m² |
| 25 Pascals | 25 N/m² |
| 50 Pascals | 50 N/m² |
| 100 Pascals | 100 N/m² |
| Reference | Pascals (Pa) | Newtons per square meter (N/m²) |
|---|---|---|
| Atmospheric pressure at sea level | 101325 Pa | 101325 N/m² |
| Healthy blood pressure (120 mmHg) | 16000 Pa | 16000 N/m² |
| A car tyre | 220000 Pa | 220000 N/m² |
| A racing bicycle tyre | 600000 Pa | 600000 N/m² |
The pascal is the SI unit of pressure, written Pa. It is defined as one newton of force spread over one square metre, and it is named after Blaise Pascal, whose experiments with barometers in the 1640s established that air has weight and that its pressure falls with altitude. The General Conference on Weights and Measures adopted the name in 1971.
It is a remarkably small unit. Atmospheric pressure at sea level is 101,325 pascals, so the pressure everyone lives under is a six-figure number, and almost every practical use of the unit therefore carries a prefix. That awkwardness is not a design fault but a consequence of coherence: the newton and the square metre were fixed first, and the pascal is whatever falls out of dividing one by the other.
Acoustics is the field where bare pascals are natural. The reference pressure for the decibel scale is twenty micropascals, taken as the quietest sound a healthy young ear can detect, and ordinary conversation is around 0.02 pascals of sound pressure. The threshold of pain sits near 63 pascals, so the entire range of human hearing spans about six orders of magnitude in this unit.
Everyday objects give a sense of the scale. A sheet of office paper lying flat presses on the desk with about 0.8 pascals. A gentle breeze exerts a few pascals on a wall, and the pressure difference that drives ventilation through a building is typically between ten and fifty. Anything a person can feel as force is already in the thousands.
Prefixed forms carry the real work. Weather uses hectopascals, which are numerically identical to the older millibars, so a forecast reading of 1013 needed no relearning. Engineering uses kilopascals for tyre and fluid pressures, and materials science uses megapascals and gigapascals for strength and stiffness, where one megapascal is one newton per square millimetre.
The pascal also appears wherever a stress rather than a pressure is meant, since the two have the same dimensions. Young's modulus, yield strength and shear stress are all quoted in pascals or their multiples, which is why a single unit spans the pressure in a tyre and the stiffness of steel.
One pascal equals 1 newton per square metre, 0.01 millibars, about 0.0000099 atmospheres, or about 0.000145 pounds per square inch.
The newton per square metre is a unit of pressure equal to one pascal. Its symbol is N/m². The two are not merely equivalent but identical: the pascal is the name given to this combination, and before the General Conference on Weights and Measures adopted that name in 1971 the SI unit of pressure had no name at all and was written out in full.
Both forms survive because they do different work on the page. The pascal is compact and reads as a unit in its own right, which suits a measurement. The newton per square metre shows its dimensions, which suits a calculation, because it makes visible that multiplying by an area in square metres will give a force in newtons.
Structural engineering leans on the second property constantly. Floor loads are specified in kilonewtons per square metre, with about 1.5 for a dwelling, 3 for an office and 5 for a place of assembly, and multiplying that figure by the floor area gives directly the load in kilonewtons that the beams must carry. Written as kilopascals the same numbers would be correct but would hide the step.
Snow and wind follow the same convention. Snow load is given in kilonewtons per square metre, from a few tenths in a mild climate to several in the mountains, and wind pressure on a facade likewise. Because those loads are combined with dead weight, which is naturally a force, keeping everything in newtons avoids the need to convert anything.
The construction repeats one prefix down. A newton per square millimetre is exactly one megapascal, which is why material strengths appear on drawings as N/mm² as often as MPa. The pattern is worth recognising: whenever a document writes force over area rather than naming a pressure unit, it is because the writer expects the reader to multiply.
Nothing else distinguishes the two forms. Any value in newtons per square metre can be written as pascals without change, and any conversion table treats them as one entry. The choice is a matter of what the number is about to be used for.
One newton per square metre equals 1 pascal, 0.01 millibars, 0.00001 bar, or about 0.000145 pounds per square inch.