Standing on one foot
All your weight, about 700 N, on one foot of 0.02 m². That is why a single-leg stand digs deeper into wet sand.
Pressure p = F/S
Force per unit area. The same weight on a smaller patch digs in harder.
Get force from F = m·a. Related: work.
Result
Enter values — the result shows up here.
How it works
p = F / S. Same person on a stiletto versus a snowshoe: area changes, weight does not. Smaller S at the same force means higher pressure.
1 Pa = 1 N/m². Atmosphere ≈ 101 kPa. US mode also shows psi. For heels and snowshoes, kPa (or MPa when the area is tiny) stays readable.
Pressure is force spread over area. The same ~700 N person on a stiletto versus a snowshoe leaves a different print because S changes. 1 atm ≈ 101 kPa.
A tyre gauge reads gas pressure inside; this calculator does mechanical contact F/S (for example a simplified tyre patch on asphalt). Both are useful; they answer different questions.
How to use
- Enter force.
- Enter area > 0.
- Read Pa/psi.
- Compare areas on the chart.
Formula
p = F ÷ S
Real-life examples
Stiletto
The same 700 N on a stiletto heel of 0.0001 m². Pressure spikes so hard that parquet floors have every right to worry.
Snowshoe
Those 700 N again, now spread across a 0.15 m² snowshoe. Pressure drops and the snow suddenly carries you.
Bottle jack
A bottle jack at work: 20000 N on a 0.01 m² piston. Tiny area, huge pressure, and the car rises anyway.
Book on a desk
A thick atlas resting on the desk: a mere 15 N over 0.04 m². Pressure so gentle the desk never even notices.
Vice jaws
Vice jaws clamping 5000 N onto a 0.0005 m² contact. Megapascals appear and the workpiece gives in locally.
Tyre contact patch
A quarter of the car on one tyre: 4000 N on a contact patch of roughly 0.008 m². Your whole grip on the road, palm-sized.
Nail tip
A hammer blow puts 100 N on a nail tip of 0.000002 m². Pressure so extreme the wall simply gives way.
Elephant model
A model elephant: 40000 N of weight over 0.3 m² of four broad feet. Less pressure than a stiletto heel makes.
Suction cup
A suction cup on tile: about 50 N of hold over 0.005 m². Enough to carry a towel, letting go only with that loud pop.
Board on mud
A wheel sinks into mud, so you slide a board under it: 800 N spreads over 0.2 m² and the car stops digging itself in.
Thumb on a thumbtack
Your thumb presses a tack with 20 N; the point measures 0.000001 m². The corkboard accepts it without a fight.
Frequently asked questions
Pa, kPa, bar: how do they relate?
1 Pa = 1 N/m². 1 kPa = 1000 Pa. 1 bar ≈ 100 kPa, near one atmosphere (~101 kPa). For heels and snowshoes, kPa (or MPa when the area is tiny) stays readable.
What about psi in US mode?
1 psi ≈ 6895 Pa. US mode may also show psi so you can compare with bike or car gauges. Remember: gauge psi is air inside the tyre, not always the same as contact-patch F/S on the road.
Why does a heel sink while a snowshoe does not?
Heel area is tiny, so p = F/S spikes at the same weight. A snowshoe spreads those ~700 N over a large S: pressure drops and snow holds. It is the cleanest everyday picture of the formula.
Is tyre pressure the same as this formula?
Related, not identical. A gauge reads the gas pressure inside. Contact F/S is a simplified "force on the patch" story. Both are useful; they answer different questions.
What if area is zero?
Division by zero. A mathematical point contact is an idealisation; real tips still have some area. Enter S > 0, even 0.000002 m² for a nail point.
How do I get force from body mass?
When standing, F ≈ m·g (g ≈ 9.81 m/s²). A 70 kg person is about 700 N. Divide by one foot, two feet, or snowshoe area: that is why one-leg stands feel harsher on soft ground.
What about fluid pressure ρgh?
Different chapter: fluid pressure grows with depth. Here you have mechanical F/S: vice jaws, nails, jacks, snow. Do not mix ρgh with shoe area unless you are doing a lake problem.
When do results jump to MPa?
When F is large and S is tiny: vices, nails, hydraulics. 5000 N on 0.0005 m² is 10 MPa. Metal yields locally, wood splits. Prefixes just shorten the writing.
How do I estimate shoe contact area?
Roughly: sole length × width in metres, or the outline on paper. For stiletto-versus-snowshoe comparisons, an order of magnitude is enough; you do not need square-millimetre precision.
Why chart different areas?
To show that at fixed F, pressure falls as S grows. Same weight, different footwear: stiletto to snowshoe. One glance explains snow, mud, and soft floors.