Pressure Conversion Calculator

The Ultimate Guide to Pressure Conversions

Pressure, defined as the force applied perpendicular to the surface of an object per unit area, is a fundamental quantity in science and engineering. We encounter it constantly, from the weather reports we hear to the air in our car tires. Because pressure is critical in so many diverse fields—from meteorology to hydraulics to diving—a variety of units have been developed to measure it. Our Pressure Conversion Calculator is designed to be a fast, accurate, and easy-to-use tool to help you navigate between these different units effortlessly.

How to Use the Pressure Converter

Our tool is built for simplicity and speed. All conversions are performed instantly as you type, with no need to click a "calculate" button.

1. Select an Input Unit: Choose the field corresponding to the unit you want to convert from. For instance, if you want to convert the pressure in a car tire, you would likely use the "Pounds per square inch (psi)" box.
2. Enter Your Value: Type the number into the selected field.
3. View Instant Conversions: As you type, all other input fields will immediately update to show the precise equivalent pressure in every other unit.
4. Clear to Reset: To start a new calculation, simply delete the number in any input box. All other fields will clear automatically, ready for your next conversion.

Understanding the Units of Pressure

To master pressure conversions, it's helpful to understand the origin and application of each major unit.

The Metric & SI Units

• Pascal (Pa): The Pascal is the official SI (International System of Units) derived unit for pressure. It is defined as one newton of force per square meter (1 N/m²). The Pascal is a very small unit of pressure; for example, standard atmospheric pressure is over 100,000 Pa. For this reason, it's often used with metric prefixes.
• Kilopascal (kPa): A kilopascal is equal to 1,000 Pascals. It is widely used in meteorology (for reporting barometric pressure), engineering, and medicine.
• Bar: While not an official SI unit, the bar is commonly used in many fields because it is approximately equal to standard atmospheric pressure. One bar is exactly 100,000 Pascals. It is frequently used in meteorology, scuba diving (to measure tank pressure), and automotive contexts.

Other Common and Imperial Units

• Standard Atmosphere (atm): This unit is defined as being exactly equal to 101,325 Pa. It was originally established as the average atmospheric pressure at mean sea level on Earth. It is a standard reference point used in chemistry, physics, and diving.
• Pounds per square inch (psi): The standard unit for pressure in the US customary system. It is the pressure resulting from a force of one pound-force applied to an area of one square inch. It is nearly ubiquitous in the United States for everyday applications, such as measuring tire pressure, water pressure in plumbing systems, and the pressure in compressed air tanks.

Absolute vs. Gauge Pressure: An Important Distinction

When discussing pressure, it's important to know the difference between two types of measurement:

• Absolute Pressure is measured relative to a perfect vacuum (which has a pressure of 0 Pa). This is a total measure of pressure.
• Gauge Pressure is measured relative to the surrounding atmospheric pressure. A tire pressure gauge, for example, reads 0 psi when it is open to the air, even though the absolute pressure is ~14.7 psi. When it reads 32 psi, it means the pressure inside the tire is 32 psi *above* the surrounding atmospheric pressure.

Our calculator converts absolute pressure values. If you are working with a gauge pressure reading, you would first need to add the local atmospheric pressure (~1 atm or ~14.7 psi) to it before converting.

Frequently Asked Questions (FAQ)

What is the difference between gauge pressure and absolute pressure?

Absolute pressure is measured relative to a perfect vacuum (0 psi or 0 Pa). Gauge pressure is measured relative to the surrounding atmospheric pressure. Therefore, Gauge Pressure = Absolute Pressure - Atmospheric Pressure. Most pressure gauges, like for tires, measure gauge pressure.

What is the standard unit of pressure?

The Pascal (Pa) is the official SI (International System of Units) derived unit for pressure. It is defined as one newton of force per square meter. Because the Pascal is a very small unit, kilopascals (kPa) and bar are often used in scientific and engineering contexts.

What is Standard Temperature and Pressure (STP)?

STP is a set of standardized conditions used to allow for comparisons between different sets of experimental data in science. The International Union of Pure and Applied Chemistry (IUPAC) currently defines STP as a temperature of 0 °C (273.15 K) and an absolute pressure of exactly 100 kPa (1 bar).