• gram = g
• milligram = 10^-3 g = mg
• microgram = 10^-6 g = ug or μg (in OceanTeacher, for simplicity, the usual symbol for micro is u)
  
• One liter (see below) of pure water has a mass of approximately 1000 grams, depending on purity, temperature and pressure.  One liter of seawater has a mass of approximately 1025 grams, depending on salinity, temperature and pressure.

• meter = m
• decimeter = 10^-1 m = dm
• centimeter = 10^-2 m = cm

• liter = l = dm³
• milliliter = 10^-3 l = ml = cm³
• cubic meter = m³ = 10³ dm³ = 10³ l
  
• The terms "liter" and "milliliter" are widely used, but the preferred units of volume are now the cubic decimeter, dm³, and the cubic centimeter, cm³.

• Mole is usally abbreviated mol in unit designation
  
• Mole = 6.02 X 10²³ molecules of a molecular substance, or atoms of an element, or ions of an ionic species in solution
  
• A mole is contained in the molecular weight or the atomic weight (as appropriate) of a substance, weight out in grams (see below for specific weights)
  

• millimol = mmol = 10^-3 mol = 6.02·10²⁰ molecules, or atoms, or ions
• micromol = umol = 10^-6 mol = 6.02·10¹⁷ molecules, or atoms, or ions 

• gram-molecular weight = mol of a molecular substance
• gram-atomic weight = mol of an element
  
• These terms were used in the older literature and should be avoided today.

• Oxygen:               15.994 g/mol (designated MMO below)
• Phosphorus:         30.974 g/mol (designated MMP below)
• Silicon:                 28.086 g/mol (designated MMSi below)
• Nitrogen:              14.0067 g/mol (designated MMN below)

• Oxygen, as O2:     31.998 g/mol (designated MMO₂ below)

• Phosphate (PO4):  94.9716 g/mol (designated MMPO₄ below)
• Silicate (SiO3):      76.0842 g/mol (designated MMSiO₃ below)
• Nitrate (NO3):       61.9887 g/mol (designated MMNO₃ below)
• Nitrite (NO2):        45.9947 g/mol (designated MMNO₂ below)

• [g/dm³] = [mol/dm³] · MMX
• [g/dm³] ~ [g/kg] · 1.025 

• For more accuracy in the /dm³-to-/kg conversion, use the true seawater density instead of 1.025.  See the note below on exact conversions.

• [ug/dm³] = [umol/dm³] · 94.9716
• [umol/dm³] = [ug/dm³] · 0.01053

Phosphate-Phosphorus

[PO4-P]

• [PO4-P] = [PO4]·MMP/MMPO₄ = [PO₄] · 0.3261
• [ug/dm³] = [umol/dm³] · 30.974
• [umol/dm³] = [ug/dm³] · 0.0322
• This quantity is usuallly calculated from the standard ionic phosphate concentration determined for non-digested seawater samples

• This quantity is calculated exactly as Phosphate-Phosphorus, above, except the sample has been completely digested before phosphate determination, insuring that particulate phosphate and non-ionic organic dissolved phosphate are included in the measurement.

• [ug/dm³] = [umol/dm3] · 78.0842
• [umol/dm3] = [ug/dm3] · 0.01280

• [SiO3-Si] = [SiO3]·MMSi/MMSiO3 = [SiO3] · 0.3691
• [ug/dm3] = [umol/dm³] · 28.086
• [umol/dm³] = [ug/dm³] · 0.03560

• [ug/dm³] = [umol/dm³] · 61.9887
• [umol/dm³] = [ug/dm³] · 0.01613

• [NO₃-N] = NO₃]·MMN/MMNO₃ = [NO₃] · 0.2259
• [ug/dm³] = [umol/dm³] · 14.0067
• [umol/dm³] = [ug/dm³] · 0.07139

• [ug/dm³] = [umol/dm³] · 45.9947 [umol/dm³] = [ug/dm³] · 0.02174

• [NO₂-N] = [NO₂]· MMN/MMNO₂= [NO₂] · 0.3045 [ug/dm³] = [umol/dm³] · 14.0067
• [umol/dm³] = [ug/dm³] · 0.07139

• [g/m³] = [ mg/l ] = [ mg/dm³]
• [mg/m³] = [ug/l] = [ug/dm³]

• 1 mol = 22.391 dm³ = 22931 cm³ at standard temperature and pressure
• 1 ml = 1 cm³ = 1/22391 mol = 0.00004461 mol = 44.61 umol
• 1 mg = 22.931/31.998 ml = 0.700 ml = 0.700 cm³
• [umol] = [ml/l] · 44.61 = [cm³/dm³] · 44.61
• [cm³/dm³] = [ml/l] = [umol] · 0.02241
• [ml/l] = [cm³/dm³] = [mg/l] · 0.700 = [mg/dm³] · 0.700
• [mg/l] = [mg/dm³] = [ml/l] · 1.428 = [cm³/dm³] · 1.428

• You can use the following equations to convert between depth in meters and pressure (p) in decibars:
  • p! = (gravity! · depth! · (1.028 + 2.4 · depth! * 10^-6))/10
  • It gives answers correct to within 0.1% (Provided by Harry Dooley of ICESInternational Council for the Exploration of the Sea)
• If you need a quick, gross estimation of p, and can accept a larger error, then you can use the formula:
  • p! = depth! · 1.007
  • This assumes that the product 2.4 · depth! · 10^-6 is negligible, which is certainly not true at great depths.
• See Physical Oceanographic Measurements for more detailed information.

• Use the Johns-Hopkins Seawater Equation of State Calculator to find the in situ densities, then divide the /dm3 values by the densities to get the /kg values.[Open the HTML source of the Calculator to find the included Java code if you want to write your own spreadsheet or database macros to perform batch conversion.]

• °F (Fahrenheit) temperature data can be converted to °C (Celsius) with the following formula:
  • °C = .55556 · (°F - 32)