• Phone: 702-591-0593
  • E-mail: Dave@doalasvegas.com 

    • SCUBA FORMULAS

    So, during your nitrox course, your instructor taught you how to calculate your MOD. You want to dive Nitrox, but you forgot how to do the calculation and you’re embarrassed to ask.  It’s okay.  I can help. Below are commonly used scuba formulas.  Find the one you forgot and no one will ever know.

    Pressure Conversion Table

    Units

    PSIG

    PSIA

    ATM

    ATA

    FSW

    FSWA

    FFW

    FFWA

    PSIG

     

    Add 14.7

    Divide by 14.7

    Add 14.7, Divide by 14.7

    Divide by 0.445

    Divide by 0.445 Add 33

    Divide by 0.432

    Divide by 0.432, Add 33

    PSIA

    Subtract 14.7

     

    Subtract 14.7, Divide by 14.7

    Divide by 14.7

    Subtract 14.7, Divide by 0.445

    Divide by 0.445

    Subtract 14.7, Divide by 0.432

    Divide by 0.432

    ATM

    Multiply by 14.7

    Multiply by 14.7, Add 14.7

     

    Add 1

    Multiply by 33

    Multiply by 33, Add 33

    Multiply by 34

    Multiply by 34, Add 34

    ATA

    Subtract 1, Multiply by 14.7

    Multiply by 14.7

    Subtract 1

     

    Multiply by 33, Subtract 33

    Multiply by 33

    Multiply by 34, Subtract 34

    Multiply by 34

    FSW

    Multiply by 0.445

    Multiply by 0.445, add 14.7

    Divide by 33

    Add 33, Divide by 33

     

    Add 33

    Multiply by 1.03

    Multiply by 1.03, Add 34

    FSWA

    Subtract 33, multiply by 0.445

    Multiply by 0.445

    Subtract 33, Divide by 33

    Divide by 33

    Subtract 33

     

    Subtract 33, Multiply by 1.03

    Multiply by 1.03

    FFW

    Multiply by 0.432

    Multiply by 0.432, add 14.7

    Divide by 34

    Add 34, Divide by 34

    Multiply by 0.97

    Add 34, Multiply by 0.97

     

    Add 34

    FFWA

    Subtract 34, Multiply by 0.432

    Multiply by 0.432

    Subtract 34, Divide by 34

    Divide by 34

    Subtract 34, Multiply by 0.97

    Multiply by 0.97

    Subtract 34

     

    PSIG = Pounds per Square Inch (Gauge)     PSIA = Pounds per Square Inch (Absolute)    ATM = Atmospheres    ATA = Atmospheres (Absolute)

    FSW = Feet of Sea Water    FSWA = Feet of Sea Water (Absolute)    FFW = Feet of Fresh Water    FFWA = Feet of Fresh Water (Absolute)

     

    “T” formula     

    Partial Pressure

    Total Pressure

    % Gas
                                            Partial Pressure = Total Pressure X % Gas

         % Gas = Partial Pressure / Total Pressure

         Total Pressure = Partial Pressure / % Gas

       

    Calculating PO2: PO2 = Depth in atmospheres absolute (ATA) X percentage O2

           PO2 = ((d+33)/33)XFO2   or  PO2 = ((d/33)+1) X FO2

           

    Calculating MOD: MOD = ((Maximum PO2 (normally 1.6 or 1.4) / % Fraction of Gas (%O2)) -1 atmosphere) X 33

            MOD=((PO2/FO2) - 1) x 33   or  MOD = (33 X PO2/FO2)-33

           

    Calculating EAD: Salt Water ((1- FO2/.79) X (D+33)) - 33

             Fresh Water ((1- FO2/.79) X (D+34)) - 34

           

    Calculating Surface Consumption Rate (SCR) in PSI/MIN:

            Salt Water:  ((PSI used/Bottom Time) X 33) / Depth + 33

            Fresh Water: ((PSI used/Bottom Time) X 34) / Depth + 34

           

    Converting SCR from PSI/MIN to Cubic Feet/MIN:

            Cubic Feet/min = SCR X Tank Volume (full)/Fill Pressure

           

    Calculating Air Consumption at depth:

            Air Consumption at Depth in Sea Water = Surface Consumption Rate / 33 X FSW

            Air Consumption At Depth in Fresh Water = Surface Consumption Rate / 34 X FFW

           

    Calculating how long a tank will last at depth:

            Tank time = Tank Volume (cubic feet) / Air Consumption at Depth (cubic feet) OR

            Tank time = Tank Pressure (PSI) / Air Consumption at Depth (PSI)

     

    Temperature Conversions:

            Degrees Celcius = .556 X (Degrees Farenhiet - 32)

            Degrees Farenhiet = (1.8 X Degrees Celcius) + 32

            Degrees Kelvin = Degrees Celcius + 273