About the Pressure Converter

The pressure converter translates between pascals, kilopascals, megapascals, bars, millibars, atmospheres, pounds per square inch, millimetres of mercury, and torr. Whether you are reading a tire pressure gauge in psi, a weather report in millibars, a medical blood pressure reading in mmHg, or an engineering specification in megapascals, this tool gives you an instant conversion in either direction.

Pressure is force per unit area, and the pascal (one newton per square metre) is the SI derived unit. Because one pascal is a very small pressure (about the pressure exerted by a dollar bill resting flat on a table), practical measurements often use kilopascals, megapascals, or bars. The atmosphere (101325 pascals) is the average atmospheric pressure at sea level, used as a reference point in many fields.

The millimetre of mercury (mmHg) and the torr are units based on the height of a column of mercury in a barometer. They are widely used in medicine (blood pressure) and vacuum physics. One atmosphere equals 760 mmHg, and one torr is defined as 1/760 of an atmosphere, making the torr and the mmHg very nearly identical.

How It Works

Each unit has a defined relationship to the pascal, the SI unit of pressure. The converter uses these factors to translate between any two units:

1 Pa    = 1 Pa                    (1 N/m^2)
1 kPa   = 1,000 Pa
1 MPa   = 1,000,000 Pa
1 bar   = 100,000 Pa                (exactly 10^5)
1 mbar  = 100 Pa                    (10^2)
1 atm   = 101,325 Pa                (standard atmosphere)
1 psi   = 6,894.757293 Pa           (1 lbf/in^2)
1 mmHg  = 133.322368421 Pa          (1 torr, approximately)
1 torr  = 133.322368421 Pa          (1/760 atm)

Every conversion proceeds in two steps: the input is multiplied by the source unit's factor to give a pressure in pascals, then divided by the target unit's factor to give the result in the target unit. The factors are exact by international agreement, with the only source of error being floating-point rounding.

The atmosphere was originally defined as the pressure exerted by a 760-millimetre column of mercury at standard gravity and zero degrees Celsius, which equals 101325 pascals. The torr was then defined as 1/760 of an atmosphere, making one torr very nearly equal to one millimetre of mercury. The bar was introduced as a convenient metric unit close to one atmosphere, defined as exactly 100000 pascals.

Worked Examples

To convert 1 atmosphere to pascals, the calculation is 1 * 101325 = 101325 Pa. To convert the same atmosphere to psi, the calculation is 101325 / 6894.757293 = 14.696 psi, which is the standard atmospheric pressure at sea level expressed in imperial units.

To convert 32 psi (a typical car tire pressure) to kilopascals, the calculation is 32 * 6894.757293 / 1000 = 220.6 kPa. This is why tire pressure gauges in metric countries show values around 220 kPa where American gauges show 32 psi.

To convert 120 mmHg (a typical systolic blood pressure reading) to kilopascals, the calculation is 120 * 133.322368421 / 1000 = 16.0 kPa. Medical blood pressure is almost universally reported in mmHg, but the SI unit is the kilopascal, and some medical literature uses both.

When to Use This Tool

Use the pressure converter whenever you need to translate between pressure units:

Reading tire pressure gauges that use psi, bar, or kPa.
Interpreting medical blood pressure readings in mmHg.
Working with weather data reported in millibars or hectopascals.
Converting engineering specifications between metric and imperial units.
Calibrating industrial pressure sensors or gauges.
Interpreting vacuum measurements in torr or pascals.
Teaching the relationships between absolute and gauge pressure units.

Limitations & Disclaimer

This converter handles absolute pressure values and does not distinguish between gauge and absolute pressure. It does not convert specialised units such as inches of water, feet of water, kilogram-force per square centimetre, or pieze. Blood pressure readings are handled as absolute mmHg values without reference to diastolic or systolic context. For medical or engineering work, verify with calibrated instruments. See our disclaimer for full details.

Frequently Asked Questions

What is the difference between gauge pressure and absolute pressure?

Gauge pressure is measured relative to atmospheric pressure, so a flat tire reads zero gauge pressure even though it contains air at one atmosphere. Absolute pressure is measured relative to a perfect vacuum, so it equals gauge pressure plus atmospheric pressure. This converter handles absolute pressure values; adjust manually if you are working with gauge pressure.

What is the standard atmosphere and why is it 101325 pascals?

The standard atmosphere is the average atmospheric pressure at sea level, defined as exactly 101325 pascals. It was originally measured as the pressure exerted by a 760-millimetre column of mercury at standard gravity and zero degrees Celsius, which equals 101325 Pa. It serves as a convenient reference point in many fields.

Why is blood pressure measured in mmHg?

Because the original blood pressure gauges (sphygmomanometers) used a column of mercury, and the height of that column in millimetres directly indicated the pressure. The unit persists in medicine even though modern devices do not use mercury, because the clinical reference values (120 over 80, for example) are well established in mmHg.

What is the difference between a bar and an atmosphere?

A bar is exactly 100000 pascals, a round metric unit chosen for convenience. An atmosphere is 101325 pascals, the actual average sea-level pressure. The two differ by about 1.3%, so they are close but not identical. The bar is used in engineering; the atmosphere is used as a reference standard.

Are mmHg and torr the same?

Almost. One torr is defined as exactly 1/760 of a standard atmosphere, which equals 133.322368421 pascals. One millimetre of mercury is the pressure exerted by a 1-millimetre column of mercury at standard gravity, which equals 133.322387 pascals. The two differ by about 0.000014%, which is negligible for all practical purposes.

How accurate are the conversions?

The conversion factors are exact by international agreement. The only source of error is floating-point rounding, which is negligible for any practical purpose. The converter displays up to eight decimal places, which is more than enough for engineering, medical, or meteorological use.

Last updated: July 21, 2026 · Author: HT99 Tools Editorial Team · Reviewed by: HT99 Tools Editorial Team