R134a PT Chart (134a Pressure Temperature)
Look up the R-134a saturation pressure for a temperature, or the temperature for a gauge reading, and print the full chart.
This R134a PT chart lists the saturation pressure of R-134a at every temperature, with a lookup in both directions. The R-134a PT chart calculator converts R-134a saturation pressure to temperature, or temperature to pressure, and shows the full pressure-temperature chart for the same refrigerant. It runs in your browser, is free, and needs no sign-up. Use it when you need a quick R-134a reading for automotive air conditioning, medium-temperature refrigeration, or a chiller, and you want the answer in psig, kPag, or bar.
R-134a is a single-component refrigerant, so each temperature maps to one pressure. The sections below explain how to read the chart, what the gauge units mean, and how to use the numbers in a service check.
How to use the R-134a PT chart calculator
- Set Refrigerant to R-134a. The result and the chart table both use this refrigerant.
- Set Convert to match your question. Choose Temperature → pressure to find the pressure at a known temperature, or Pressure → temperature to find the temperature for a gauge reading.
- Enter your value. In Temperature → pressure mode, type the temperature in Saturation temperature. In Pressure → temperature mode, enter the pressure reading and, where Gauge or absolute pressure appears, pick its unit: psig, kPag, or barg for a gauge reading, or psia, kPaa, or bara for absolute pressure.
- Set Chart units to °F and psig, °C and bar (gauge), or °C and kPa (gauge). This sets the units of the result and of the chart table.
- Read the result rows. Only the rows that apply to your mode appear.
- Under More options, change Chart table step to Auto, every 1 degree, every 2 degrees, every 5 degrees, or every 10 degrees. If you work at altitude, enter Altitude above sea level; leave it blank at sea level.
- Scroll down to the R-134a pressure–temperature chart to check nearby values.
Use the example buttons above the form to load a sample calculation. Copy link saves every input in the page address, so the same calculation reopens later. Copy result copies the result lines with a link, and Print / save as PDF includes the inputs, results, steps, and date. Reset restores the starting example.
How do you read a PT chart?
A PT chart lists the pressure at which R-134a boils or condenses at each temperature. To read it, find the temperature in the left column and read the pressure in the same row. To go the other way, find the pressure and read the temperature. From this chart, 40 °F gives 35.0 psig, 70 °F gives 71.1 psig, and 100 °F gives 124.2 psig.
The chart temperature is the real refrigerant temperature only where liquid and vapor are both present, such as in the evaporator or condenser. In a superheated suction line or a subcooled liquid line the pressure is still about the evaporator or condenser pressure, but the pipe temperature is not the chart temperature: the difference between the two is the superheat or the subcooling. The calculator computes the value for the exact temperature or pressure you enter, so you do not need to interpolate between table rows. For example, 130 °F gives 198.7 psig.
Is a PT chart in psig or psia?
A PT chart is usually given in psig, which is gauge pressure. Gauge pressure is measured relative to the surrounding air, which is 14.696 psi at sea level. Automotive AC service gauges read R-134a in psig, so the chart values match what you see on the gauge.
Absolute pressure in psia equals psig plus 14.696. At 70 °F, the chart gives 71.1 psig, which is 85.8 psia. The metric equivalents follow the same rule: kPag is gauge and kPaa is absolute. Local air pressure falls at altitude, so gauge readings shift there. Enter your altitude under More options to account for this.
How the R-134a values are calculated
The chart is not typed in from a printed table. It comes from the published equation of state for R-134a, evaluated at every whole degree Celsius, and the calculator interpolates between those points (pressure is close to a straight line on a log scale against 1/temperature, so the error is far below gauge resolution). Checked against NIST data, the values agree within 0.01 %. A few points from the chart at sea level: -20 °F: -1.8 psig; 0 °F: 6.5 psig; 20 °F: 18.4 psig; 40 °F: 35.0 psig; 70 °F: 71.1 psig; 100 °F: 124.2 psig; 120 °F: 171.2 psig.. Set your altitude under More options and the gauge values shift by the difference in atmospheric pressure.
Sources
Data and methods used by this calculator (checked October 2026):
- CoolProp equations of state (saturation data)
- NIST Chemistry WebBook, thermophysical properties of fluids (pure refrigerants, checked within 0.05 %)
- ASHRAE Standard 34 refrigerant designations and safety classes
Worked examples
| Input | Result |
|---|---|
| R-134a, 35 °F | 30.4 psig |
| R-134a, 130 °F | 198.7 psig |
| R-134a, 0 °C | 1.915 barg |
| R-134a, 30 psig | 34.56 °F |
Calculated by the tool above with these values.
Frequently asked questions
What is the pressure of R-134a at 70 °F (standing pressure)?
Standing pressure is the pressure in a system that has been off long enough for the refrigerant to settle at the surrounding temperature. At sea level, R-134a at 70 °F is 71.1 psig according to this chart.
What should R-134a pressures be when running?
There is no single correct running pressure. Readings depend on outdoor and indoor temperatures, airflow, load, and system design, so they change as conditions change. Compare your readings with the equipment manufacturer’s charging information, and use the superheat and subcooling calculator to check the system.
What is R-134a pressure at 0 °C in bar?
At 0 °C, R-134a is 1.915 barg (gauge). To see this value, set Chart units to °C and bar (gauge) and enter 0 °C in Saturation temperature.
How accurate are the values?
The calculator uses equations of state as implemented in CoolProp, which is checked against NIST data for pure fluids. Values agree with NIST within 0.01 %. For estimation only, verify critical designs against the applicable standard, and use the equipment manufacturer’s chart when one is available.
Can I use the results in a quote or service record?
Yes. Results, charts, and printouts may be used freely in commercial work such as quotes, proposals, reports, and service records. No attribution is needed.
Related tools
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- Superheat and subcooling calculator: Use it after reading a pressure to check superheat or subcooling in a running system.
- R-410A PT chart: Use it when the system uses R-410A instead of R-134a.
- R-22 PT chart: Use it for older systems that run on R-22.
- R-32 PT chart: Use it for systems charged with R-32.
- R-454B PT chart: Use it for systems charged with R-454B.
- R-404A PT chart: Use it for low- and medium-temperature refrigeration systems charged with R-404A.
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