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 - c_{1}) * p − c_{2 * }p^{2} (1)

Where

- c
_{1}= (5.92 + 5.25 * sin^{2}φ) * 10^{−3}; - c
_{2}= 2.21 * 10^{−6}; - φ is latitude in radians;
- z is depth in meters;
- p is pressure in decibars.

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

- k = (5.92 + sin
^{2}φ * 5.25) / 1000; - φ - latitude in radians;
- z - depth in meters;
- p - pressure in kPa.

In this online calculator, the Total Pressure can be used, it includes the 1 atmosphere air pressure at sea level, whence

p_{t} = p + 101.325, [kPa] (3)

To convert degrees into radians, the next formula is used:

φ = L * Π / 180 (4)

Where

- L - latitude in degrees;
- Π - 3.14159265359;
- φ - latitude in radians.