CochraneScuba Charles' Law Calculator

Charles' Law
Pressure / Volume Calculator

NOTE: This calculator is for discussion purposes only and is not intended for actual dive planning.
Refer to your certifying agency procedures to plan your dives

What is Charles' Law?

Charles Law is used to show the relationship between a gas and any pressure and temperature changes. In the Scuba diving world, we use it to show how your air (gas) consumption changes in relation to your depth (pressure) and water temperature.

What is Charles' Law used for?

Although it's more commonly used during the PADI Divemaster course and by PADI Instructors teaching the Divemaster course, Charles' Law is a valuable tool for scuba divers of all levels wanting to perform precise diving planning. Divers can determine, based on depth and temperatures, how long a cylinder of air will last. If you know your breathing rate (on the surface or at depth) you'll also be able to "fine tune" just how far that cylinder will take you.
*IMPORTANT - Understand that the amount of air in your cylinder doesn't change as you go deepershrink,

Salt Water Fresh Water
Starting Depth
Planned Diving Depth
Beginning Tank Volume (PSI)
Beginning Temperature (if known)
Temperature at depth (if known)


  1. Select either Salt or Fresh Water
  2. Enter your starting depth (typically 0 for the surface), starting volume (pressure in your cylinder) & temperature
  3. Enter your planned depth and the temperature at that depth, if you know it
  4. Click the Calculate button. The program will calculate the ending volume for you

*Note - The following defaults will be used unless a different value is used:
    Starting depth - 0
    Starting volume - 1
    Starting temperature - 70 F
    Ending temperature - 70 F

NOTE - Temperature is in Degrees F, Depth in Feet

To calculate the ending volume by hand use the following formula.

                      P1  X  V1       P2  X  V2
                     ____________ = ____________
			  T1             T2
P1 is the starting depth in feet
V1 is the starting pressure in psi
T1 is the starting temperature in F
P2 is the ending depth in feet
V2 is the ending pressure in psi
T2 is the ending temperature in F

For more information, contact:
Tim B Cochrane
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