Gas Constant Units Converter
Free Gas constant units Converter for chemical & molecular units. Enter a value to see equivalent measurements across systems.
Gas Constant Units Converter
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Formula: Converted R = (Input / R_source) x R_target
Worked example โ 8.314 J/(mol*K) = 0.08205 L*atm/(mol*K)
Formula
Converted R = (Input / R_source) x R_target
Divide the input value by the known gas constant in the source units to get a dimensionless multiplier. Then multiply that ratio by the gas constant expressed in target units to obtain the converted value.
Worked Examples
Example 1: SI to Liter-Atmosphere Form
Problem:Convert 8.314 J/(mol*K) to L*atm/(mol*K).
Solution:Ratio = 8.314 / 8.314462618 = 0.999944 Result = 0.999944 x 0.0820573661 = 0.082053 L*atm/(mol*K)
Result:8.314 J/(mol*K) = 0.08205 L*atm/(mol*K)
Example 2: SI to Calorie Form
Problem:Convert 8.314462618 J/(mol*K) to cal/(mol*K).
Solution:Ratio = 8.314462618 / 8.314462618 = 1.0 Result = 1.0 x 1.987204 = 1.987204 cal/(mol*K)
Result:8.314 J/(mol*K) = 1.987 cal/(mol*K)
Frequently Asked Questions
What is the universal gas constant and why does it have different unit forms?
The universal gas constant (R) is a fundamental physical constant that appears in the ideal gas law PV = nRT. Its numerical value changes depending on which units are used for pressure, volume, temperature, and amount of substance. In SI units, R = 8.314462618 J/(mol*K), but when pressure is measured in atmospheres and volume in liters, R = 0.08206 L*atm/(mol*K). The physical quantity remains identical; only the numerical expression changes with the measurement system.
How do you convert the gas constant between different unit systems?
To convert R between unit systems, you use the ratio method. First divide your input value by the known R value in the source units to get a dimensionless ratio (which should be close to 1 for the standard gas constant). Then multiply by the R value in the target units. For example, to convert 8.314 J/(mol*K) to cal/(mol*K), compute (8.314 / 8.314462618) times 1.987204 to get approximately 1.987 cal/(mol*K).
When would you use calories per mole Kelvin versus joules per mole Kelvin?
The calorie-based form of R (1.987 cal/(mol*K)) is commonly used in thermochemistry and biochemistry where energy changes are traditionally reported in calories or kilocalories. The joule-based SI form (8.314 J/(mol*K)) is preferred in physics and modern chemistry. Older chemistry textbooks and some pharmaceutical literature still use calories extensively. Using the wrong form in a calculation will produce results off by a factor of approximately 4.184, which is the number of joules per calorie.
What is the relationship between the gas constant and Boltzmann constant?
The gas constant R equals the Boltzmann constant (kB) multiplied by Avogadro number (NA). Specifically, R = kB times NA = 1.380649e-23 J/K times 6.02214076e23 per mol = 8.314462618 J/(mol*K). While R is used for molar quantities (per mole of particles), kB is used for individual molecules. This relationship is fundamental in statistical mechanics and connects macroscopic thermodynamic properties to microscopic particle behavior.
Where does the value 0.08206 L*atm/(mol*K) come from?
It follows directly from the SI value by converting the energy unit. One litre-atmosphere is 0.001 m3 multiplied by 101,325 Pa, which is exactly 101.325 joules. Dividing 8.314462618 J/(mol*K) by 101.325 J per L*atm gives 0.0820573661 L*atm/(mol*K), which rounds to the familiar 0.08206. Chemists favour this form because gas-law problems are usually posed with pressure in atmospheres and volume in litres, so no further unit juggling is needed inside PV = nRT.
Why is the torr-based value about 62.36 L*Torr/(mol*K)?
Because one standard atmosphere is defined as exactly 760 torr, the millimetre-of-mercury pressure unit still common in vacuum work and older laboratory manuals. Multiplying the litre-atmosphere form of 0.0820573661 by 760 gives 62.3636 L*Torr/(mol*K). Use this version when your manometer or vacuum gauge reads in torr, so pressure enters the ideal gas law unconverted and you avoid an extra rounding step.
What is the difference between the universal gas constant and a specific gas constant?
The universal constant R is molar: it applies to one mole of any ideal gas. A specific gas constant is per unit mass and is obtained by dividing R by the molar mass, so R_specific = R / M. For dry air with a molar mass near 0.02896 kg/mol, that gives roughly 287 J/(kg*K), the value used throughout aerodynamics and HVAC work. Specific constants differ for every gas, whereas R is the same for all of them.
What are the lb-mol and the degree Rankine used in the imperial forms?
A pound-mole is simply 453.59237 gram-moles, the amount of substance whose mass in pounds is numerically equal to the relative molecular mass, so it is 453.59237 times larger than a gram-mole. The degree Rankine is the absolute temperature scale built on Fahrenheit-sized degrees, each 5/9 of a kelvin. Applying both conversions to the SI value gives about 2,095 J/(lbmol*degR), which divided by 1.35582 joules per foot-pound yields the 1,545.35 ft*lbf/(lbmol*degR) that appears in US natural gas engineering.
Why do the calorie and BTU forms of R have almost the same number?
It is a near coincidence built into the way both units were defined from heating water. Going from cal/(mol*K) to BTU/(lbmol*degR) multiplies by the pound-to-gram ratio and the Fahrenheit degree size, and the calorie-to-BTU ratio very nearly cancels them. The residual difference between 1.98720 and 1.98588 comes from the BTU being an International Table unit while the calorie here is the thermochemical one. Do not treat them as interchangeable in precise work.
Is the gas constant an exact number or a measured one?
It has been exact since the 2019 revision of the SI. The Boltzmann constant was fixed at exactly 1.380649 x 10^-23 J/K and the Avogadro constant at exactly 6.02214076 x 10^23 per mole, and because R is their product it inherits an exact value of 8.31446261815324 J/(mol*K). Before 2019 R carried an experimental uncertainty inherited from measurements of the triple point of water and acoustic gas thermometry.
References
Reviewed for accuracy by Manoj Kumar, Mathematics Educator ยท Editorial policy
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