# What is the pressure?

Computes pressure from force and area (P = F ÷ A), or the force from the pressure and area, or the area from the force and pressure, in pascals, kPa, bar, psi and atmospheres.

- Page: https://www.acalculator.org/physics/pressure-calculator
- JSON spec: https://www.acalculator.org/physics/pressure-calculator.json
- Version: 1e44f11b38f9

## Default answer

Example with the default inputs (Find Pressure, Force 112.404471549855 lbf, Area 387.50077500155 in²): The answer is P = 2000 Pa (0.290075 psi).

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| find | Find | Which of pressure, force and area to work out from the other two. |
| F | Force | The force pressing straight onto the surface. |
| A | Area | The area the force is spread over. |
| P | Pressure | The pressure on the surface. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| result | Answer | The value worked out, to 6 significant figures, in its main units. |
| pa | Pressure (Pa) | The pressure in pascals (N/m²). |
| kpa | Pressure (kPa) | The pressure in kilopascals. |
| psi | Pressure (psi) | The pressure in pounds-force per square inch. |
| bar | Pressure (bar) | The pressure in bar (100,000 Pa). |
| atm | Pressure (atm) | The pressure in standard atmospheres (101,325 Pa). |
| newtons | Force (N) | The force in newtons. |
| lbf | Force (lbf) | The force in pounds-force. |
| m2 | Area (m²) | The area in square meters. |
| in2 | Area (in²) | The area in square inches. |

## Method

P = F ÷ A; F = P × A; A = F ÷ P.

## Assumptions

- The force presses straight onto the surface (perpendicular to it) and is spread evenly over the area.
- Exact unit sizes: 1 lbf = 4.4482216152605 N; 1 in² = 0.00064516 m²; 1 psi = 6,894.757293168361… Pa; 1 bar = 100,000 Pa; 1 atm = 101,325 Pa; 1 mmHg = 133.322387415 Pa.

## Worked examples

1. find = pressure, F = 500, A = 0.25 gives pa = 2,000, kpa = 2, result = P = 2000 Pa (0.290075 psi). Source: OpenStax, University Physics Volume 1, §14.1 Fluids, Density, and Pressure (p = F ÷ A), https://openstax.org/books/university-physics-volume-1/pages/14-1-fluids-density-and-pressure.
2. find = pressure, F = 4.448222, A = 0.000645 gives psi = 1, pa = 6,894.757293. Source: NIST SP 811, Appendix B.8 (1 lbf = 4.4482216152605 N; 1 in = 0.0254 m; 1 atm = 101,325 Pa; 1 bar = 100,000 Pa), https://www.nist.gov/pml/special-publication-811.
3. find = force, P = 101,325, A = 1 gives newtons = 101,325, atm = 1. Source: OpenStax, University Physics Volume 1, §14.1 Fluids, Density, and Pressure (p = F ÷ A), https://openstax.org/books/university-physics-volume-1/pages/14-1-fluids-density-and-pressure; NIST SP 811, Appendix B.8 (1 lbf = 4.4482216152605 N; 1 in = 0.0254 m; 1 atm = 101,325 Pa; 1 bar = 100,000 Pa), https://www.nist.gov/pml/special-publication-811.
4. find = area, F = 700, P = 200,000 gives m2 = 0.0035, result = A = 0.0035 m² (5.42501 in²). Source: OpenStax, University Physics Volume 1, §14.1 Fluids, Density, and Pressure (p = F ÷ A), https://openstax.org/books/university-physics-volume-1/pages/14-1-fluids-density-and-pressure.

## FAQ

### What is the formula for pressure?

Pressure is force divided by area: P = F ÷ A. A force of 500 N spread over 0.25 m² gives 500 ÷ 0.25 = 2,000 Pa (2 kPa).

### What is a pascal?

One pascal (Pa) is one newton per square meter. It is a small unit: air pressure at sea level is 101,325 Pa, so kPa, bar and psi are more common in practice.

### How do I convert psi to pascals?

1 psi is one pound-force on one square inch: 4.4482216152605 N ÷ 0.00064516 m² = 6,894.757 Pa. So 30 psi is about 206.8 kPa.

### How do I find the force from pressure?

Multiply the pressure by the area: F = P × A. One atmosphere (101,325 Pa) on 1 m² pushes with 101,325 N, about 22,779 lbf.

### Why does a sharp knife cut better?

The same force on a smaller area gives a higher pressure. Halve the area and the pressure doubles.

### What is the difference between bar and atm?

1 bar is exactly 100,000 Pa. 1 standard atmosphere is 101,325 Pa, about 1.013 bar.

## Sources

- OpenStax, University Physics Volume 1, §14.1 Fluids, Density, and Pressure (p = F ÷ A; 1 Pa = 1 N/m²). https://openstax.org/books/university-physics-volume-1/pages/14-1-fluids-density-and-pressure (retrieved 2026-10-03)
- NIST SP 811, Appendix B.8 Factors for Units Listed Alphabetically (pound-force per square inch, bar, standard atmosphere, millimeter of mercury). https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b8 (retrieved 2026-10-03)