The calculations in this online calculator are based on the work "Practical Conversion of Pressure to Depth" by Peter M. Saunders. The formula (1) is the adopted equation of state for seawater (T = 0°C, Salinity = 35 NSU) by Millero et al., 1980 (this is so-called "UNESCO formula").
z = (1 - c1) * p − c2 * p2 (1)
Where
To get pressure from depth, the equation (1) is converted into equation (2):
p = ((1 - k) - ((1 - k)2 - (8.84E-6 * z))0.5) / (4.42E-6) * 10 (2)
Where
In this online calculator, the Total Pressure can be used, it includes the 1 atmosphere air pressure at sea level, whence
pt = p + 101.325, [kPa] (3)
To convert degrees into radians, the next formula is used:
φ = L * Π / 180 (4)
Where