Boyles Law (final pressure)

vCalc Reviewed
Equation / Last modified by KurtHeckman on 2018/04/10 16:54
vCalc.Boyles Law (final pressure)

The Boyle's Law for Final Pressure calculator computes the final pressure (P2) of a fixed amount of gas at a fixed temperature after it undergoes a change in state from an initial volume (V1) and pressure (P1) to a final volume (V2).

INSTRUCTIONS: Choose units and enter the following:

  • (P1) This is the initial pressure
  • (V1) This is the initial volume
  • (V2) This is the final volume

Final Pressure (P2): The calculator return the pressure in pascals.  However this can be automatically converted to compatible units via the pull-down menu.

The Math / Science

Boyle's Law is expressed as: V1 • P1 = V2 • P2.  The Boyle's Law formula for the final pressure is:

P2 = V1•P1 / V2



Boyle’s Law states that the volume of a gas varies inversely with its pressure if temperature is held constant.  Boyle's Law (sometimes known as Mariotte's Law) describes the relationship a perfect gas where mass and temperature are kept constant.  Under these conditions, the volume of the gas will vary inversely with the absolute pressure.  This equation calculates a pressure given the corresponding elements of the equivalence; Initial pressure, Initial volume, and temperature.

Boyle's Law can be expressed as:
         `PV = "constant"`  
         `p_1*V_1 = p_2*V_2`

  • P = absolute pressure (Pa, psi...)
  • V = volume (`m^3`, `ft^3`...)


Boyles Law has obvious visible effects on our everyday life, describing the phenomena associated with pressurized cans, balloons and similar mechanical devices that contain gases under pressure.  One example is a weather balloon.  As the balloon rises in the atmosphere, the pressure outside the balloon decreases, allowing the pressure inside the balloon to expand the balloon.  As the balloon rises high enough the external pressure can drop enough that the balloon expands beyond its material's ability to stretch and the balloon will break. Boyle's Law basically defines that pressure and volume relationship both inside and outside the balloon.

Another example of Boyle's Law is the simple syringe.  As you draw back the plunger on the syringe, you increase the volume in the chamber of the syringe causing a vacuum in the syringe which in turn sucks-in liquid on the other side of the needle .