  The integral length scale ($\mathcal{L}$) is considered to be characteristic
of the largest motions of a turbulent flow, and as such, it is an input
parameter in modern and classical approaches of turbulence theory and numerical
simulations. Its experimental estimation, however, could be difficult in
certain conditions, for instance, when the experimental calibration required to
measure $\mathcal{L}$ is hard to achieve (hot-wire anemometry on large scale
wind-tunnels, and field measurements), or in 'standard' facilities using active
grids due to the behaviour of their velocity autocorrelation function
$\rho(r)$, which does not in general cross zero. In this work, we provide two
alternative methods to estimate $\mathcal{L}$ using the variance of the
distance between successive zero crossings of the streamwise velocity
fluctuations, thereby reducing the uncertainty of estimating $\mathcal{L}$
under similar experimental conditions. These methods are applicable to variety
of situations such as active grids flows, field measurements, and large scale
wind tunnels.
