Pressure Calculator
Calculate pressure based on force applied and surface area.
Formula
P = F / A
Pressure equals Force divided by Area.
Worked Examples
Example 1: Standing on one foot
Problem:700N person on 0.02m² foot
Solution:700 / 0.02
Result:35,000 Pa
Frequently Asked Questions
What is pressure and how is it calculated?
Pressure is the force acting perpendicular to a surface divided by the area over which that force is spread, written P = F / A. Force is measured in newtons and area in square metres, so pressure comes out in newtons per square metre. Because area sits in the denominator, the same force concentrated on a smaller patch produces a much larger pressure, which is why a drawing pin pierces a board that your thumb alone cannot.
What is the SI unit of pressure?
The pascal, symbol Pa, defined as one newton per square metre. A pascal is a very small unit in everyday terms, so practical work uses multiples: the kilopascal (1 kPa = 1,000 Pa) for weather and tyres, and the megapascal (1 MPa = 1,000,000 Pa) for material strength. For reference, a sheet of A4 paper resting flat exerts roughly 1 pascal on the desk beneath it.
How do I convert between pascals, bar, psi and atmospheres?
One standard atmosphere is 101,325 Pa exactly, which equals 101.325 kPa, 1.01325 bar, 14.696 psi, and 760 mmHg. One bar is defined as exactly 100,000 Pa, so bar and atmosphere are close but not identical. To go from psi to kilopascals multiply by 6.895; to go from kilopascals to psi divide by the same figure. Pressure Calculator applies these factors automatically.
What is atmospheric pressure and why does it change with altitude?
Atmospheric pressure is the weight of the column of air above you pressing down, about 101,325 Pa at sea level. Climb higher and there is less air overhead, so the pressure falls: roughly 90 kPa in Denver at 1,600 m and about 26 kPa at the cruising altitude of an airliner. The fall is exponential rather than linear, dropping by about half for every 5,500 m of ascent.
How does contact area change the pressure a force produces?
Pressure is inversely proportional to area, so halving the contact area doubles the pressure for the same force. A 700 N person standing on two shoes covering 0.03 m2 exerts about 23 kPa, but the same person on a single stiletto heel of 0.0001 m2 exerts 7 MPa, enough to dent a hardwood floor. Snowshoes work on the opposite principle, spreading weight to keep pressure below what the snow can support.
What is the difference between gauge and absolute pressure?
Gauge pressure is measured relative to the surrounding atmosphere, so a tyre gauge reading zero means the tyre is at atmospheric pressure, not a vacuum. Absolute pressure is measured from a perfect vacuum. The two are related by Absolute = Gauge + Atmospheric, so a tyre reading 32 psi gauge is actually at about 46.7 psi absolute at sea level. Thermodynamic calculations almost always require absolute pressure.
What is psi and where is it used?
Psi stands for pounds-force per square inch and is the customary pressure unit in the United States. It appears on tyre placards, air compressors, hydraulic systems and domestic water supplies. One psi equals 6,894.76 pascals. Typical car tyres run 30 to 35 psi, domestic water mains deliver 40 to 60 psi, and a hydraulic press may operate above 3,000 psi.
How does pressure work in a liquid?
In a static fluid, pressure increases with depth according to P = rho x g x h, where rho is the fluid density, g is 9.81 m/s2 and h is depth. Fresh water adds roughly 9.81 kPa for every metre of depth, so a diver at 10 m experiences about one extra atmosphere. Pressure at a given depth acts equally in all directions and does not depend on the shape or width of the container.
Why do your ears pop on an aircraft?
The middle ear is a sealed air pocket behind the eardrum. As a cabin climbs the outside pressure falls, so the trapped air is momentarily at a higher pressure and pushes the eardrum outward, which you feel as fullness. Swallowing or yawning opens the Eustachian tube and lets the pressures equalise, producing the pop. On descent the imbalance reverses and the eardrum is pushed inward instead.
What is standard pressure and how does it differ from standard atmosphere?
The standard atmosphere is 101,325 Pa, the historical reference used for altimetry and most engineering tables. IUPAC, however, defines standard pressure for thermochemistry as exactly 100,000 Pa, or 1 bar, a change made in 1982. The difference is only 1.3 percent but it matters when quoting standard enthalpies or gas molar volumes, so check which convention a data table is using.