Hyperbaric Pressure Converter: ATA to PSI, kPa, mmHg

Hyperbaric Pressure Converter: ATA to PSI, kPa, mmHg, and Depth

Hyperbaric pressure is stated in ATA, atmospheres absolute. 1 ATA is normal sea-level pressure. A chamber at 1.3 ATA adds about 4.4 psi above the atmosphere, and a chamber at 2.0 ATA adds about 14.7 psi. Use the converter to move between units and to see how pressure and oxygen concentration combine.

Pressure converter

Chamber pressure (ATA)

From 1.0 to 6.0

Oxygen in breathing gas (%)

Room air is 21%

Gauge pressure: 4.4 psi above atmosphere
Absolute pressure: 19.1 psi
Kilopascals: 131.7 kPa
Millimeters of mercury: 988 mmHg
Equivalent sea water depth: 9.9 feet
Inspired oxygen partial pressure: 0.27 ATA (207 mmHg)

For education and unit conversion only. This tool does not recommend a pressure, a breathing gas, or a session schedule. Inspired oxygen partial pressure is a simplified calculation (pressure multiplied by oxygen fraction) and is not a measurement of oxygen levels in blood or tissue.

Common hyperbaric pressures in every unit

Common hyperbaric pressures converted between units, breathing room air
ATA	psi (gauge)	kPa	mmHg	Sea water depth	Inspired O2, room air
1.0	0.0	101.3	760	0.0 ft	0.21 ATA
1.3	4.4	131.7	988	9.9 ft	0.27 ATA
1.5	7.3	152.0	1,140	16.5 ft	0.32 ATA
2.0	14.7	202.7	1,520	33.0 ft	0.42 ATA
2.4	20.6	243.2	1,824	46.2 ft	0.50 ATA
3.0	29.4	304.0	2,280	66.0 ft	0.63 ATA
4.0	44.1	405.3	3,040	99.0 ft	0.84 ATA

The last column assumes room air (21% oxygen). Breathing a gas with a higher oxygen concentration raises the inspired oxygen partial pressure further at the same chamber pressure.

Pressure and oxygen concentration are separate variables

Hyperbaric therapy starts with a physical fact: the person is inside an environment pressurized above normal atmospheric pressure. Raising the pressure raises the partial pressure of every gas being breathed, including oxygen, even when the breathing gas is ordinary air.

Oxygen concentration is a second, independent variable. Increased pressure raises the partial pressure of inspired oxygen, and a higher inspired oxygen concentration raises it further. Knowing a chamber's pressure does not tell you what gas was breathed, so a statement such as "1.3 ATA" describes pressure only.

The full exposure, or dose, also depends on time at pressure, how often sessions happen, and the total number of sessions. Two studies can both use the word HBOT while delivering very different doses. The research library lists each study's pressure, breathing gas, session length, and schedule for that reason.

How the conversions work

psi (absolute) = ATA x 14.696
psi (gauge) = (ATA - 1) x 14.696
kPa = ATA x 101.325
mmHg = ATA x 760
Sea water depth in feet = (ATA - 1) x 33
Inspired oxygen partial pressure = ATA x oxygen fraction

Chamber gauges show gauge pressure, the amount added above the surrounding atmosphere. Research papers usually state absolute pressure in ATA. Converting between the two is the most common source of confusion when reading chamber specifications.

Hyperbaric Pressure FAQ

How many psi is 1.3 ATA?

1.3 ATA is about 19.1 psi absolute, which is about 4.4 psi above normal atmospheric pressure (gauge pressure). Chamber gauges read gauge pressure, so a chamber at 1.3 ATA shows roughly 4 psi.

What does ATA mean?

ATA stands for atmospheres absolute. 1 ATA is normal atmospheric pressure at sea level. 2 ATA is twice that pressure. ATA includes the atmosphere you are already under, which is why it is called absolute.

Is pressure the same as oxygen concentration?

No. Pressure and oxygen concentration are separate variables. Pressure is how much the surrounding environment is compressed. Oxygen concentration is the fraction of the breathing gas that is oxygen. Both affect the partial pressure of inspired oxygen.

What is the difference between absolute and gauge pressure?

Absolute pressure counts the atmosphere itself, so sea level is 1 ATA or 14.7 psi absolute. Gauge pressure counts only the pressure added above the atmosphere, so sea level is 0 psi gauge.

Does this converter tell me what pressure to use?

No. It converts units. A qualified clinician determines whether hyperbaric therapy is appropriate and sets the pressure, breathing gas, session length, and frequency for an individual.

Compare chambers by operating pressure

OxyHealth makes portable chambers that operate at 1.3 ATA and clinical hard-sided chambers that operate up to 4.0 ATA. Higher pressure is not automatically better and lower pressure is not automatically safer. The right chamber depends on intended use and a clinician's protocol.