Ideal gas law states that product of a pressure and volume is proportional to the product of temperature and amount of gas. The coefficient of proportionality is called ideal gas constant and does not depend on the type of the gas. Ideal gas law applies to gases in conditions where molecular volume and inter-molecular forces are negligible. This law is a generalization of the combined gas law over different types of gases. Ideal gas law could also be derived from the kinetic theory. Ideal gas law wiki article

Solve for	Equations
P
V
n
T
N
M
m
q

Pressure (P)		atmosphere (standard) atmosphere (technical) bar barye (cgs unit) centimetre of mercury centimetre of water (4 C) foot of mercury (conventional) foot of water (39.2 F) inch of mercury (conventional) inch of water (39.2 F) kilogram-force per square millimetre kip per square inch micron (micrometre) of mercury millimetre of mercury millimetre of water (3.98 C) pascal (SI unit) pieze (mts unit) pound per square foot pound per square inch poundal per square foot short ton per square foot torr
Volume (V)		acre-foot acre-inch barrel (Imperial) barrel (petroleum) barrel (U.S. dry) barrel (U.S. fluid) board-foot bucket (Imperial) bushel (Imperial) bushel (U.S. dry heaped) bushel (U.S. dry level) butt, pipe coomb cord (firewood) cord-foot cubic fathom cubic foot cubic inch cubic metre (SI unit) cubic mile cubic yard cup (breakfast) cup (Canadian) cup (metric) cup (U.S. customary) cup (U.S. food nutrition labeling) dash (Imperial) dash (U.S.) dessertspoon (Imperial) drop (Imperial) drop (Imperial) (alt) drop (medical) drop (metric) drop (U.S.) drop (U.S.) (alt) fifth firkin fluid drachm (Imperial) fluid dram (U.S.); U.S. fluidram fluid scruple (Imperial) gallon (beer) gallon (Imperial) gallon (U.S. dry) gallon (U.S. fluid; Wine) gill (Imperial); Noggin gill (U.S.) hogshead (Imperial) hogshead (U.S.) jigger (bartending) kilderkin lambda last litre load minim (Imperial) minim (U.S.) ounce (fluid Imperial) ounce (fluid U.S. customary) ounce (fluid U.S. food nutrition labeling) peck (Imperial) peck (U.S. dry) perch pinch (Imperial) pinch (U.S.) pint (Imperial) pint (U.S. dry) pint (U.S. fluid) pony pottle; quartern quart (Imperial) quart (U.S. dry) quart (U.S. fluid) quarter; pail register ton sack (Imperial); bag sack (U.S.) seam shot strike (Imperial) strike (U.S.) tablespoon (Australian metric) tablespoon (Canadian) tablespoon (Imperial) tablespoon (metric) tablespoon (U.S. customary) tablespoon (U.S. food nutrition labeling) teaspoon (Canadian) teaspoon (Imperial) teaspoon (metric) teaspoon (U.S. customary) teaspoon (U.S. food nutrition labeling) timber foot ton (displacement) ton (freight) ton (water) tun wey (U.S.)
Temperature (T)		degree Celsius degree Delisle degree Fahrenheit degree Newton degree Rankine degree Reaumur degree Romer degree Kelvin (SI unit)
Boltzmann's constant (k)	(std) 1.38E-23 1.38E-23	J/K
Number of moles (n)
Number of molecules (N)
Mass (m)		atomic mass unit, unified atomic unit of mass, electron rest mass bag (coffee) bag (Portland cement) barge carat carat (metric) clove crith dalton dram (apothecary; troy) dram (avoirdupois) electronvolt gamma grain gram grave hundredweight (long) hundredweight (short); cental kilogram (SI unit) kip mark mite mite (metric) ounce (apothecary; troy) ounce (avoirdupois) ounce (U.S. food nutrition labeling) pennyweight point pound (avoirdupois) pound (metric) pound (troy) quarter (Imperial) quarter (informal) quarter, long (informal) quintal (metric) scruple (apothecary) sheet slug; geepound; hyl stone ton, assay (long) ton, assay (short) ton, long ton, short tonne (mts unit) wey
Molar mass (M)		atomic mass unit, unified atomic unit of mass, electron rest mass bag (coffee) bag (Portland cement) barge carat carat (metric) clove crith dalton dram (apothecary; troy) dram (avoirdupois) electronvolt gamma grain gram grave hundredweight (long) hundredweight (short); cental kilogram (SI unit) kip mark mite mite (metric) ounce (apothecary; troy) ounce (avoirdupois) ounce (U.S. food nutrition labeling) pennyweight point pound (avoirdupois) pound (metric) pound (troy) quarter (Imperial) quarter (informal) quarter, long (informal) quintal (metric) scruple (apothecary) sheet slug; geepound; hyl stone ton, assay (long) ton, assay (short) ton, long ton, short tonne (mts unit) wey
Gas constant (R)	(std) 8.3144621 8.3144621	J/(mol*K)
Density (q)		gram per millilitre kilogram per cubic metre (SI unit) kilogram per litre ounce (avoirdupois) per cubic foot ounce (avoirdupois) per cubic inch ounce (avoirdupois) per gallon (Imperial) ounce (avoirdupois) per gallon (U.S. fluid) pound (avoirdupois) per cubic foot pound (avoirdupois) per cubic inch pound (avoirdupois) per gallon (Imperial) pound (avoirdupois) per gallon (U.S. fluid) slug per cubic foot