Combined gas law is a result of unification of Charles's law, Boyle's law and Gay-Lussac's gas laws. In isolation each of these laws relate one thermodynamic variable to another while holding everything else constant. For instance, Charles's law asserts that as long as pressure is held constant, volume and temperature are proportional to each other. Boyle's law states that pressure and volume are inversely proportional as long as temperature is fixed. Gay-Lussac's law postulates a proportionality between temperature and pressure at a constant volume. Combined gas laws is a direct consequence of these three laws, it states that product of pressure and volume divided by the temperature of the system is constant. Combined gas law wiki article

Solve for	Equations
P1
V1
T1

Pressure (P1)		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
Pressure (P2)		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 (V1)		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.)
Volume (V2)		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 (T1)		degree Celsius degree Delisle degree Fahrenheit degree Newton degree Rankine degree Reaumur degree Romer degree Kelvin (SI unit)
Temperature (T2)		degree Celsius degree Delisle degree Fahrenheit degree Newton degree Rankine degree Reaumur degree Romer degree Kelvin (SI unit)