The underlying flame physics can be understood with the help of an idealized model consisting of a uniform one-dimensional tube of unburnt and burned gaseous fuel, separated by a thin transitional region of width  in which the burning occurs. The burning region is commonly referred to as the flame or flame front. In equilibrium, thermal diffusion across the flame front is balanced by the heat supplied by burning.
Two characteristic timescales are important here. The first is the thermal diffusion timescale , which is approximately equal to
where  is the thermal diffusivity. The second is the burning timescale  that strongly decreases with temperature, typically as
where  is the activation barrier for the burning reaction and  is the temperature developed as the result of burning; the value of this so-called "flame temperature" can be determined from the laws of thermodynamics.
For a stationary moving deflagration front, these two timescales must be equal: the heat generated by burning is equal to the heat carried away by heat transfer. This makes it possible to calculate the characteristic width  of the flame front:
thus
Now, the thermal flame front propagates at a characteristic speed , which is simply equal to the flame width divided by the burn time:
This simplified model neglects the change of temperature and thus the burning rate across the deflagration front. This model also neglects the possible influence of turbulence. As a result, this derivation gives only the laminar flame speed—hence the designation .