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Refrigerants & gases

R-600a (isobutane) · C4H10

R-600a (isobutane (2-methylpropane), CAS 75-28-5) is a single-component refrigerant; this page gives its saturation pressure and saturated liquid and vapour densities from -40 to 60 °C.

Saturation pressure and saturated liquid and vapour densities are computed from CoolProp==6.6.0 - reference Helmholtz equation of state for IsoButane and tabulated over -40–60 °C.

Also known as
Isobutane, 2-Methylpropane, HC-600a, R600a, i-butane
CAS number
75-28-5
Tabulated range
-40–60 °C · saturation line
Designation
Refrigerant
R-600a
Chemical name
isobutane (2-methylpropane)
GWP (100-yr)
1
ASHRAE 34 class
A3

GWP 1 — WMO 2022 100-year GWP (basis attributed by the U.S. EPA Technology Transitions GWP Reference Table). U.S. EPA - Technology Transitions GWP Reference Table. U.S. Environmental Protection Agency, Technology Transitions GWP Reference Table: R-600a (isobutane) 100-year GWP = 1 (table reference WMO 2022). https://www.epa.gov/climate-hfcs-reduction/technology-transitions-gwp-reference-table

ASHRAE 34 A3 — ANSI/ASHRAE Standard 34 safety group classification. ANSI/ASHRAE Standard 34 - Designation and Safety Classification of Refrigerants. ANSI/ASHRAE Standard 34-2022, Designation and Safety Classification of Refrigerants: R-600a (isobutane) assigned safety group A3.

At 25 °C (saturation)
reference snapshot
Saturation pressure
3.507bar
Pressure
350.7kPa
Gauge
36.2psig
Liquid density
550.6kg/m³
Vapour density
9.13kg/m³
Explore

Read the saturation line either way

Set a temperature to read its saturation pressure and densities, or set a pressure to read the saturation temperature. Every number is interpolated from the committed table below and clamped to the validated -40–60 °C range — nothing is computed from a property model in your browser.

Interactive explorer

Values are interpolated along the tabulated saturation line below — both the temperature and the pressure stay within the validated -40–60 °C range and are never extrapolated.

25 °C
Saturation temp
25.0 °C
Saturation pressure
3.507 bar
Pressure
350.7 kPa
Gauge pressure
36.2 psig
Liquid density
550.6 kg/m³
Vapour density
9.13 kg/m³
Saturation pressure (bar) vs temperature (°C) — R-600a.
Saturation table

Every tabulated point

Saturation pressure (absolute, shown in kPa and bar, with the gauge value in psig at standard atmosphere) and the saturated liquid and vapour densities at each temperature. A negative psig is a partial vacuum below one atmosphere.

T °Cp kPap barp psigρ liq kg/m³ρ vap kg/m³
-4028.70.287−10.5624.10.88
-3536.80.368−9.4618.91.10
-3046.60.466−7.9613.61.37
-2558.40.584−6.2608.31.69
-2072.50.725−4.2602.92.07
-1589.00.890−1.8597.42.51
-10108.51.0851.0591.93.01
-5131.01.3104.3586.33.59
0157.01.5708.1580.64.26
5186.71.86712.4574.85.01
10220.62.20617.3568.95.87
15259.02.59022.9563.06.83
20302.23.02229.1556.97.91
25350.73.50736.2550.69.13
30404.74.04744.0544.310.48
35464.84.64852.7537.811.99
40531.25.31262.3531.213.67
45604.56.04573.0524.415.53
50684.96.84984.6517.417.59
55773.07.73097.4510.219.89
60869.28.692111.4502.722.43
Typical values

R-600a saturation pressure at a glance

At -20 °C, R-600a saturation pressure is about 0.72 bar (72 kPa; −4.2 psig). At 0 °C, R-600a saturation pressure is about 1.57 bar (157 kPa; 8.1 psig). At 25 °C, R-600a saturation pressure is about 3.51 bar (351 kPa; 36.2 psig). At 40 °C, R-600a saturation pressure is about 5.31 bar (531 kPa; 62.3 psig).

Sources

Where the numbers come from

Every value on this page is computed by a deterministic equation of state — none is entered by hand. The generating method and the references it is checked against:

  • ▸NIST Chemistry WebBook, SRD 69 - Thermophysical Properties of Fluid Systems (REFPROP-derived saturation tables), isobutane (CAS 75-28-5)
  • ▸CoolProp 6.6.0 - reference Helmholtz equation of state for isobutane (Buecker & Wagner, 2006)
  • ▸U.S. EPA - Technology Transitions GWP Reference Table (100-year GWP, WMO 2022 reference)
  • ▸ANSI/ASHRAE Standard 34-2022 - Designation and Safety Classification of Refrigerants

Model: CoolProp==6.6.0 - reference Helmholtz equation of state for IsoButane · Generated 2026-06-07

The committed data file for this page is published as JSON on GitHub under CC BY 4.0.

Validation

Checked against cited values

The equation of state is cross-checked against independently cited saturation points. The page is published only because every check passes.

Property / pointSaturation pressure · 25 °C
Cited reference value350.67 kPa
Model computed350.67 kPa
Error vs reference0% (tolerance 1%)

NIST Chemistry WebBook, SRD 69 - Thermophysical Properties of Fluid Systems. NIST Chemistry WebBook, SRD 69, Thermophysical Properties of Fluid Systems, isobutane (R-600a, 2-methylpropane) (CAS 75-28-5), saturation curve at 25 degC: saturation pressure = 350.67 kPa. https://webbook.nist.gov/cgi/fluid.cgi?ID=C75285&Action=Page

Property / pointSaturated liquid density · 25 °C
Cited reference value550.65 kg/m3
Model computed550.65 kg/m3
Error vs reference0% (tolerance 1%)

NIST Chemistry WebBook, SRD 69 - Thermophysical Properties of Fluid Systems. NIST Chemistry WebBook, SRD 69, Thermophysical Properties of Fluid Systems, isobutane (R-600a, 2-methylpropane) (CAS 75-28-5), saturation curve at 25 degC: saturated liquid density = 550.65 kg/m3. https://webbook.nist.gov/cgi/fluid.cgi?ID=C75285&Action=Page

Limitations

Before you use these numbers

  • ▸CoolProp reference Helmholtz equation of state (Buecker & Wagner, 2006) for isobutane. Saturation properties only, tabulated from -40 to +60 degC; superheated and single-phase data are out of scope for this page. The critical point is 134.67 degC / 3629.0 kPa, well above the table top, so every tabulated state is sub-critical. Values are for preliminary design; verify against vendor data for critical service.
  • ▸Saturation properties only — these are two-phase (saturation-line) values; superheated and sub-cooled single-phase data are out of scope for this page. The critical point is 134.67 °C / 3629 kPa, above the tabulated range.
  • ▸Values are tabulated only inside the -40–60 °C range shown; the equation of state is not extrapolated beyond it here.
  • ▸Use for preliminary design; verify for critical service.
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