In an electrolyte or a colloidal suspension, the Debye length for a monovalent electrolyte is usually denoted with symbol κ
where
* I is the ionic strength of the electrolyte in number/m units,
* ε is the permittivity of free space,
* ε is the dielectric constant,
* k is the Boltzmann constant,
* T is the absolute temperature in kelvins,
*  is the elementary charge,
or, for a symmetric monovalent electrolyte,
where
* R is the gas constant,
* F is the Faraday constant,
* C is the electrolyte concentration in molar units (M or mol/L).
Alternatively,
where  is the Bjerrum length of the medium in nm,
and the factor  derives from transforming unit volume from cubic dm to cubic nm.
For deionized water at room temperature, at pH=7, λ ≈ 1μm.
At room temperature (), one can consider in water the relation:
where
* κ is expressed in nanometres (nm)
* I is the ionic strength expressed in molar (M or mol/L)
There is a method of estimating an approximate value of the Debye length in liquids using conductivity, which is described in ISO Standard, and the book.